GEOLOGY

AND

GEOMORPHOLOGY

FOR THE COURSE OF

CE 501: GEOLOGY AND GEOMORPHOLOGY

WORLD UNIVERSITY OF BANGLADESH DEPARTMENT OF CIVIL ENGINEERING

september2013

© This copy is written for the students of 2nd semester of Dept. of civil engineering for 3 credit course of CE 501: Geology and Geomorphology. It is not for sell or any kind of financial profit making. All rights whatsoever in this book are strictly reserved and no portion of it may be reproduced any process for any purpose without the written permission of the owners. -----------------------------------------------------------------------------------------------------

AUTHOR S M Tanvir Faysal Alam Chowdhoury, B.Sc. (Civil)

Lecturer in Dept. of Civil Engineering

WORLD UNIVERSITY OF BANGLADESH

Written by: Students of: Batch 57C (It is a course work task) Dept. of Civil Engineering World university of bangladesh

DEFINITION OF GEOMORPHOLOGY:

The study of the landforms of the earth including their history and process of origin. This is

the systematic examination of the landforms and their interpretation as records of the past

history.

The information is utilized by members of the different groups of sciences such as those

related to geography, geology, geophysics, in addition to geomorphology.

Actually interest of different groups overlap.

No clear line of distinction among these group.

ASPECTS OF GEOMORPHOLOGY:

It establishes relation between land forms and the underlying rocks and is concerned

with the interaction between the denudation process and rock forming.

It studies the evolution of landscape, which is often called the “Denudation

chronology”.

It studies the actual process of erosion which gives rise of land forms.

PRINCIPAL ZONES OF EARTH:

Atmosphere: It is the gaseous envelop encircling the earth. Distribution of heat, pressure and

water vapor content within this envelope gives rise to the global weather and climate.

Hydrosphere: This is the water envelop on solid earth. Elements of this zone are river, lake,

ocean etc.

Lithosphere or Geosphere: This is the solid earth. It has three distinct divisions, which are as

follows:

A thin outer shell or crust (16~40 km thick)

An inner zone called mantle (2900 km thick)

Core: This is divided into two distinct parts:

Liquid outer core nickel iron (2200 km thick0

A solid zone called core (1300 km radius)

[Radius of the earth is about 6400 km=3960 miles]

Biosphere: The life zone of earth. This is the zone of influence upon the geomorphic process.

Form the small plankton to man is included on it.

GEOMORPHIC AGENTS AND PROCESS:

Those physical and chemical process which effect a modification of the earth’s surficial form

is called geomorphic process.

A geomorphic agent is any natural medium, which is capable of sccuring and transporting

earth materials thus running water including both concentrated and unconcentrated run-off,

groundwater, glaciers, wind and movements within bodies of standing water including waves,

currents and tide fall in this group.

IS GRAVITY A GEOMORPHIC AGENT?

Most of the geomorphic agents originate within the earth’s atmosphere. And also directed by

the force of gravity. Gravity is not a geomorphic agent because it cannot secure and carry

away materials. It is better though a directional force.

AN OUTLINE OF THE GEOMORPHIC PROCESS:

Geomorphic processes are primarily classified into three categories depending on the origin.

Those are

Epigene or exogenetic

Hypogene or endogenetic

Extraterrestrial

The geomorphic process which originate outside the earth’s crust are called and

others originating within the earth’s crust are designated as

The topographic effects of the impact of meteorites (piece of rock or metal that has reached

the earth’s surface from outer space) do not fall within either of the above classes and are

termed extraterrestrial, which means from beyond the limits of the earth’s domain.

Any form of plant or animal life that

drift in or float on water bodies

GEOMORPHIC PROCESSES:

A. Epigene or exogenetic processes

I. Gradation

a) Degradation

i) weathering

ii) mass wasting or gravitative transfer

iii) Erosion (including transpor3tation) by

1. running water

2. ground water

3. waves, currents, tides and tsunami

4. winds

5. glaciers

b) Aggradation by

1. running water

2. ground water

3. waves, currents, tides.

4. wind

5. glaciers

c) work of organisms including man

B. Hypogene or endogenetic processes.

1. Diastrophism

2. Vulcanism

C. Extraterrestrial processes:

Fall of meteorites

All actual movements of the earth’s solid crust of any kind

of degree. The crust movement falls into two categories:

1. Slow movements, 2. Sudden movements (e.g.:

earthquake)

Includes all sorts of volcanic activities together with the movements

of the motion rock or magma into or towards the earth surface.

NOTES ON DIFFERENT GEOMORPHIC PROCESSES:

a) Gradation

It includes all the processes that tend to bring the surface of the lithosphere (the rocky crust

of the earth) to a common level. Gradation process belongs to two categories:

1. Degradation Level down

2. Aggradation Level up

b) Weathering

This may be defined as the changes that take place in the minerals and rocks at near the

surface of the earth in response to the atmosphere, to water and to plant and animal life. This

is a static process and does not involve the removal or seizure of materials by a transporting

agency.

c) Mass wasting

Involve the bulk transfer of the masses of rock derbies down slopes under the direct influence

of gravity. Mass wasting is usually aided by the pressure of water but the water is not in such

an amount so that it can be considered as a transporting medium. (we can think that the

process is initiated by the action of water but the material is actually carried by the action of

gravity)

d) Impact of meteorites

The uniqueness of the process lies in the fact that they were produced by the extraterrestrial

agents although earth’s gravitational attraction was responsible for the fall of meteorites.

e) Topographic effects of organisms

Man-made road cuts and fills and many other excavations profoundly modify the earth’s

surface. Explosives (bombs) may become a distinctive and prevalent type of land form if

modern welfare continues.

RELATION BETWEEN WEATHERING AND EROSION:

Weathering EROSION

Production of rock waste in place under virtually static condition.

Transportation of rock waste from site of its formation.

Both the processes are parts of a single process called Denundation lowering of the surface of the earth.

Weathering aided crosion by weakening and disintegrating rocks.

Erosion in turn aids weathering by removing the cover of soil and loose derbies and exposing them to the weather

Weathering can take place without subsequent erosion and erosion is possible without previous weathering. Weathering is a preparatory process but neither a prerequisite nor necessarily followed by erosion.

RUNOFF AND RUNOFF RELATIONS

INTRODUCTION:

The water reaching the surface of the earth in the form of precipitation reaches the stream

ultimately. From the point where precipitation reached the earth surface it may take different

paths on its way to the stream.

Precipitation is the general term for all forms for moisture emanating from the cloud and

falling on the ground.

Some part of the water flow over the land surface an reaches the stream immediately after

the precipitation. The other part of the precipitation infiltrates through the soil surface and

flows through the soil surface to reach the stream.

COMPONENTS OF THE TOTAL FLOW:

Visualization of the three main routes of travel is very easy. These are

Overland flow or surface runoff.

Interflow or subsurface run off

Ground water flow

Surface runoff: It is that part of water which travels over the ground surface to the channel

without infiltrating or percolating to the water table. The term channel as used here indicates

all sort of depressions which is capable of holding water for a short period of time after the

rainfall.

Sub-surface runoff: it is that portion of the total flow which after infiltrating the soil surface

move laterally through the upper soil layer until it enters the channel. Subsurface runoff

reaches the channel more slowly than the surface runoff and hence reaches the stream later.

Ground water flow: some portion of the precipitation percolates downward until it reaches

the ground water table. This ground water storage may discharge into the stream if the water

table intersects the stream channels of the basin. This discharge is called the Ground Water

Flow.

Runoff: runoff is the collective term which refers to all the three components of the total

flow, i.e., surface runoff, sub-surface runoff and the ground water flow.

In practice it is customary to consider the total flow to be divided inti two parts such as

Direct runoff

Basic flow

Direct runoff is presumed to consist mainly of overland flow and a substantial portion of sub

surface runoff whereas the base-flow considered to be consisting of the ground water flow.

FACTORS AFFECTING RUNOFF:

1. Characteristics of precipitation:

a) Type of precipitation: Precipitation generally occurs in the form of rain or a snow depending

on which the runoff pattern varies. Rain produces immediate runoff whereas that in the form

of snow produces runoff at a slower rate.

b) Rainfall intensity: If the rainfall intensity increases the runoff also increases. For example if

the rainfall increases by the four times the runoff may increase by nine times.

a) b)

Fig: 2

An intense rain as shown in fig. 2(a) will definitely produce much more runoff than produced

by the uniform rainfall shown as shown in Fig. 2(b) provided the infiltration capacity remains

the same throughout the storm period.

c) Duration of rainfall: Duration of rainfall is important regarding the fact that the infiltration

capacity of the soil goes on decreasing as rainfall continues for longer duration. As the

infiltration decreases the surface runoff increases. Thus rain of a longer duration may produce

a considerable runoff even when the intensity is mild.

d) Rainfall distribution: all the above discussion is made based on the assumption that rainfall

is evenly distributed over the whole catchment area which does not happen in reality. In

reality, rain falls on a small part of the whole basin. For small drainage basins the peak flow

are the results of intense rain falling over the small areas whereas for the large basins the

peak flows are results of storms of less intensity but covering a large area.

e) Soil Moisture deficiency: The runoff depends on the soil moisture present at the time of

rainfall. If the rain occurs after a long dry spell of time, the soil is dry and it can absorb huge

amount of water and thus intense rain may fail to produce appreciable runoff. On the other

hand, if the rain falls after a rainy season, the soil will already be wet and there will be less

infiltration and eve small rainfall may cause appreciable runoff.

WHAT IS DIFFERENCE BETWEEN INFILTRATION ANF PRELOCATION?

f) Direction of the prevailing storm: if the direction of the storm is in the same direction as

the direction of the water movement in the drainage basin then the water will stay in the

drainage basin for a shorter time. This is due to the fact that the runoff will be more compared

to that if direction of storm is opposite to that of the direction of the water movement.

g) Various climatological factors such as temperature, wind, humidity etc. affect the losses

from the drainage basin. If losses are more then runoff will be less.

2. CHARACTRASTISTICS OF THE DRAINAGE BASIN:

a) Size of the basin: if the area of the basin is large then the total flow will take more time to

pass the outlet and the peak will be reduced.

b) Shape of the basin: The shape of the drainage basin also governs the rate at which water

enters the stream. “Form Factor” and “Compactness Coefficient” generally express the shape

of the basin.

Form factor=𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑤𝑖𝑑𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑏𝑎𝑠𝑖𝑛

𝐴𝑥𝑖𝑎𝑙𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑏𝑎𝑠𝑖𝑛=

𝐵

𝐿

The axial length (L) is the distance between the outlet and the most remote point on the basin

and the average width (B) is obtained by dividing the total area (A) by the axial length. So,

Form factor = 𝐵

𝐿 =

𝐴𝐿⁄

𝐿 =

𝐴

𝐿2

Compactness coefficient is defined as

Compactness coefficient = 𝑃

𝐶

Where, P= perimeter of the basin

C = Circumfluence of the circle whose area is the same as the area of the basin.

If ‘A’ is the area of the basin and ‘r’ is the radius of the equivalent circle then

A = 𝐴 = 𝜋𝑟2 r= √𝐴𝜋⁄

Circumfluence = 2𝜋𝑟 =2𝜋√𝐴𝜋⁄ = 2√𝐴𝜋

Compactness coefficient = 𝑃(2√𝐴𝜋 )

⁄

Where, P = perimeter of the basin, A = area of the basin

COMPUTATUIN OF RUNOFF:

RATIONAL METHOD

Introduction:

The rational method is an intensity based rainfall method, meaning that it can be used to predict popular method in stream system analysis.

Objectives of rational method:

Many hydrologic design problems require simply an estimation of peak flow rate generated by a river system under specified conditions. In such problems, the general shape of the flood hydrograph and the time of occurrence of the peak flow rate are no special significance and need not be taken into account. In such cases the rational method can be applied to estimate the peak flow rate.

Also when adequate data are not available this method can be applied.

Assumptions:

# The rainfall is uniform both spatially and temporarily.

# The drainage area is small.

# The duration of the rainfall is equal to the catchment’s time of concentration.

# Peak flow occurs when the entire catchment area is contributing.

# The recurrence interval of the peak discharge is equal to that of the rainfall intensity.

Rational formula:

Rational formula:

Peak discharge, Q = kICA

Where, Q = Peak discharge in 𝑚3

𝑠 or

𝑓𝑡3

𝑠

A = Area of the catchment (acres or hectares)

I = Rainfall intensity with the selected recurrence interval, T years and

duration equal to the catchment’s time of concentration.

K = a factor of proportionality

= 0.278 when ‘A’ in K𝑚2 and ‘I’ in mm/hr. = 0.00278 when ‘A’ in hectares and ‘I’ mm/hr.

= 1.0 when ‘A’ in 𝑚2 and ‘I’ in m/s C = Co-efficient of run-off which depends on the type of area, soil condition, soil covers, storage, depressions etc.

Area type Description ‘C’ values

Business Downtown Neighborhood

0.07-0.095 0.50-0.70

Residential

Single family Multiunit detached Multiunit attached Suburban resident Apartment 1.2 acre lots or more

0.30-0.50 0.40-0.60 0.60-0.75 0.25-0.40 0.50-0.70 0.30-0.45

Lawns, Heavy soils Flat 2% Average, 2-7% Steep>7%

0.13-0.17 0.18-0.22 0.25-0.35

Industrial Light Heavy

0.50-0.80 0.60-0.90

Lawns, Sandy soils

Flat 2% Average, 2-7% Steep>7%

0.05-0.10 0.10-0.15 0.15-0.20

Pavement

Asphalt/Concrete Brick Drives and walks

0.70-0.95 0.70-0.85 0.75-0.85

THE NATURE OF A RIVER VALLEY

Valley: Elongated lowland between ranges of mountains, hills, or other uplands, often having a river or stream running along the bottom.

RIVER DEVELOPMENT

The river development may be divided into two parts. The development of the feature of an individual valley, and The development of a system of drainage, composed of many individual valleys.

Valley Development: A valley takes the form through the operation of three simultaneous processes. These are: 1) Valley deepening, 2) Valley widening, and 3) Valley lengthening.

1) VALLEY DEEPENING: Is effected by the following factors:

a) Hydraulic Actions: The impact or pressure of running water, under certain circumstances, may cause a considerable amount of erosion even without the aid of other tools. Thus a stream flowing through relativity loose or soft materials may, by this process, cut back its bank or push off its materials from the bottom of the channel. The agent is the running water.

b) Corrosion or abrasion of the floor of the valley: It refers to the mechanical wearing away of rocks by the rubbing, grinding and bumping action of rocks by the rubbing, grinding, and bumping actions of rock fragments.

c) Pothole drilling along the valley floor and the base of water falls: A pothole is a deep, round hole worn in rock by loose stones whirling in strong rapids or waterfalls.

d) Corrosion or solution: Many rocks and minerals are soluble in water and their solubility is increased by the presence of small amounts carbonic acid glass and oxygen which are found in all water in nature. Solution of bed rock material into the stream water deepens the valley.

2) VALLEY WIDENING: Valley width is the linear distance between the two sides of it. This is expressed along with the different locations of the valley reach. Valley widening may be accomplished in the following ways:

a) Lateral erosion: Stream in a valley may remove materials from the base of the valley side through hydraulic and corrosive action. This results in the over steepening of the valley floor which favors slumping of the materials into the stream.

b) Rainwash or sheetwash: Contributes in an important way in valley widening. Loose weathered materials are washed down the valley side by rain.

c) Gullying on valley sides: Gullies are mini streams with which every fresh supply of water, become deeper longer and wider. After a time gullies are large enough to be called valleys.

d) Incoming tributaries contribute to the valley widening even though they are nothing more than overgrown gullies.

3) VALLEY LENGTHINING: May take place in three ways. These are:

By the process of headward erosion.

Through increase in size of their meanders.

Valley also may lengthen at their termini.Uplift of the land or lowering of the lake level will result in extension of the valley from across the newly exposed land.

CLASSIFICATION OF VALLEYES:

A. According to the stage in the geomorphic cycle valleys are classified as:

1. Young 2. Mature 3. Old. This classification rather based on the characteristics developed at different stages in their evolution.

A young valley is narrower, and steep sided because down-cutting had greatly been predominant over the process of valley widening till this stage.

Figure: Cross profile of valleys at different stage of development.

A mature valley is wider, less steep sided and usually deeper than a young valley. It generally has numerous, relatively large, well-developed tributaries.

An old valley shows gently sloping sides, moderate to shallow depth and fewer tributaries than the mature valley.

B. Genetic classification:

1. Consequent valley 2. Subsequent valley 3. Insequent valley 4. Resequent valley 5. Obsequent valley.

A consequent valley is one whose course was supposedly determined by the initial slope of the land and natural irregularities of the surface.

Subsequent valleys are those whose courses have been shifted from the original consequent ones to belts of more rapidly erosive rocks. These streams develop independently of the original (initial) topography and are determined and regulated by erosion proceeding differently upon the bedrock formations according to the differences in hardness, structure and resistance to erosion of the formations.

Insequent valley are those which shows no apparent adjustment to lithological control. These streams do not appear to depend upon either initial depressions or weakness in the rock. There might be two possibilities in this regard: Either the streams owe their courses completely to chance, or They are guided by lithological difference too small to be detected by man.

Valleys which presumably drain in direction, opposite to that of the original consequent valleys are defined as obsequent. Now a days they are defined as streams which flows in a direction opposite to that of the geological dip of the beds.

C. Based on controlling structures: It is possible to classify the valleys on the basis of the geological structures, which have controlled their development. Based on this classification we have: 1. Homoclinal valleys 2. Anticlinal valleys 3. Synclinal Valleys 4. Fault valleys 5. Fault line valleys 6. Joint valleys

1. Homoclinal valleys: This type of valleys were known as the monoclinal valleys in the earlier times. These are strike valleys which follow the beds of weaker rock along the flanks of folds. 2. Anticlinal valleys: If the valleys follow the axes of breached anticlines. 3. Synclinal Valleys: These follow the axes of the breached synclines. 4. Fault valleys: Valley whose positions are determined by the faults may be of two types. One of these is a fault valley incases when then streams follow depressions consequent upon falling. The other type is the fault line valleys. 5. Fault line valleys: If the subsequent valleys follow a fault line. 6. Joint valleys: Some valley courses or portion of the valley courses are controlled by the major joint systems and are classes as the joint valleys.

RIVER TRANSPORTATION

Activities of running water: The water that flows along the river does the following works:

It transports the derbies

It erodes the river Channel deeper into the land

It deposits sediments at various points along the valley or delivers them to lakes or oceans

River transportation: River transportation is the ability of the river to carry along the particles that a stream picks up directly from its own channel or that is supplied to it by slope wash, tributaries or mass movement.

Factors affecting the transportation power of river:

Size of particle to be carried

Volume of total land

Velocity of river

Some important definitions:

Load: The amount of material that a river carries at any time is called its load.

Capacity: The total amount of material a river is capable of carrying under ant given set of conditions is called the capacity of the river.

Capacity of a river varies approximately with the third power of velocity if a fair proportion of all grain sizes are available, with a higher power if all the materials are fine grained and with a lower power if the material is coarse. The capacity is a function of discharge and velocity.

Competence: The maximum size of particle that a river can carry is called its competence. The competence of a river is a statement of its ability to move materials in terms of material size. Competence is a function of velocity only. The diameter of a particle that a river can move varies approximately with the square of the stream velocity.

CLASSIFICATION OF LOAD

Load carried in solution

Load carried mechanically as sediment

Dissolved load: These are the soluble materials and are carried in solution in the form of ions. The amount of dissolved load depends upon 1) Climate, 2) Season, 3) Geologic setting.

Suspended load: This is the load carried mechanically as sediment. These are the particles of solid matter that are swept along in the turbulent current of the stream and remain in suspension. The amount of this load Depends upon 1) intensity of turbulence of water and 2) terminal velocity of each individual particle.

Bed load: These are solid particles, which move along the riverbed. Bed load mainly consists of gravel and sand.

MOVEMENT OF BED LOAD:

Particles in bed load move in three ways: 1. By saltation 2. By Rolling 3. By sliding

1. Saltation: A particle moving by saltation jumps from one point of the stream to another. First, it is picked up by a current of turbulent water and flung upwards and if it is too heavy to remain in suspension, it drops to the stream floor again at some spot downstream.

2. Rolling and sliding: Some particles are too large and too heavy to be picked up by the water current. But they may be pushed along the streambed and depending upon their shape, they move forward either by rolling or by sliding.

CHANNEL CHANGES IN THE FLOOD:

We think the flood as the change in the height of water surface and subsequent inundation but apart from that change occurs in the stream bed which we can not see because of the turbidity of water flowing through the stream.

Fig: Stage discharge behavior in unsteady flow condition.

The figure above, represents the unsteady behavior of stage-discharge relationship at a location of the stream. The maximum stage and the maximum discharge occur at different times. The changes of the channel bed form that take place during the flood need a clear understanding of this unsteady behavioral pattern.

River channel changes in configuration with this rising and falling stage.

At first the bed am be build up by large amounts of bed load supplied in the stream during the first phase of heavy runoff. [Observe the elevated bed level as result of it]. This stage disappears soon.

The bed is actively deepened by scour as the stem stage rises. This is quite interesting to mark the lowest elevation of the bed level at the highest water level

In the next stage which can be identified by the falling stage of the stage discharge curve, the stage to fall and the bed is built back up by the deposition of the bed load.

In the example shown in the figure, about 10ft of thickness of alluvium was reworked, that is, moved about in the complete cycle of rising and falling stage.

When the flood crest has passed after the decrease in the discharge, the capacity of the stream transport load also declines. Some of the particles that are in motion come to rest on the bed in the form of sand and gravel bars. First the largest boulders and cobblestones will cease rolling, then the pebbles and gravels and then the sand. When restored to low stage, the water may become quite clear with only a few grains of sand rolling along the bed where the current is still fast enough.

CONCEPT OF EQUILIBRIUM AND GRADED STREAM: As an idealized concept, “an equilibrium condition” means the supply of load to a stream from its drainage basin such that it exactly matches the capacity of stream to transport. In this type of stream the hydraulic factors are changing continuously to bring about a state of equilibrium. This sort stream is called the graded stream. Based on the concept of Mackin, a geomorphologist:

A graded stream is one which the slope is delicately adjusted over a period of years to provide, along with the available discharge and prevailing channel characteristics, just the velocity required for the transportation of the load supplied to it by the drainage basin.

FACTORS CONTROLLING THE EQUILIBRIUM OF THE STREAM:

a) Stream discharge (Q): Usually measured in 𝑓𝑡3

𝑠𝑒𝑐⁄ or 𝑚3

𝑠𝑒𝑐⁄ . Dependent mainly on the climate. The relationship Q=A * 𝑉𝑚 is important.

b) Sediment discharge and the size of the sediment: Climate weathering and all processes delivering sediment to the stream determine the quantity of sediment discharge (tons/ day) and the size of the sediment. The size of grains and the structure of original rock material are also important criterion.

c) Slope: the slope adjusts automatically to provide the velocity necessary for transporting the amount and the size of the material being delivered to the stream. If the slope is too low for transporting the sediment load, deposition occurs until the slope is sufficient for transporting. If the slope is so steep that it provides a velocity greater than that necessary to transport the load, erosion reduces the slope. This new slope will provide the velocity needed to transport the sediment load.

d) Channel shape: the ratio of wide to depth is used to describe the channel shape. The interaction of discharge, amount of sediment, slope and local factors such as back erodability and channel alignment determine channel shape.

Channel slope is important in determining stream velocity and so sediment transport. Generally, as channel becomes narrow sediment transport becomes more efficient. When narrowing of a channel occurs because of deposition on the bank, erosion of bed is likely to result. Again, when the deposition of the channel bed occurs, the erosive forces on the bank increases resulting widening of the stream.

LONGITUDINAL PROFILE OF A STREAM:

The longitudinal profile of a stream is a graphic outline of the stream’s gradient along it’s course. It provides information of the elevation of the streambed at any location, the elevation being measured with respect to some fixed datum (may be w.r.t. MSL)

The longitudinal profile is function of the following variables: Discharge, Load delivered to the channel, Size of derbies, Velocity of flow, flow resistance, depth of flow, width of the channel, slope of the channel.

Fig.: Schematic diagram of longitudinal profile of stream

EQUATION OF LONGITUDINAL PROFILE: Assumption: The tendency of a stream to erode at any particular point-along its profile is directly proportional to the height of the stream above the base level.

If,

H= Elevation above base level or MSL in feet X=Distance downstream from source in mile

Then based on assumption:

𝑑𝐻

𝑑𝑋∝ -H

Or, 𝑑𝐻

𝑑𝑋 = -bH

Or, 𝑑𝐻

𝐻 = -bdX

Or, log𝑐 𝐻 = -bX+log𝑐 𝐶

Or, log𝑐 𝐻 - log𝑐 𝐶 = -bX

Or, log𝑐 𝐻/𝐶 = -bX

Or, H/C = 𝑒−𝑏𝑋

Is the equation of the longitudinal bed profile.

READJUSTMENT OF THE STREAM GRADE:

A graded stream delicately adjusted to its environment of supply of water and rock waste from the upstream sources is highly sensitive to changes in those controls. Changes in climate and in land surface of the water shade bring changes in discharge and load at downstream points and these changes in turn require channel adjustment.

Effect of increase in bed load: [Increase of bed load beyond stream capacity accumulation of coarse sediment on the stream bed elevation of stream bed] Aggredatoin

As consequence of aggredation:

In the upstream direction: Reduces the channel slope in the u/s direction reduction of stream capacity in the reach accumulation of the bed materials in the u/s direction/

In the downstream direction: The channel slope is increased velocity increases more bed material dragged downstream.

Aggradation changes the channel cross section from a narrow and deep form to a wide an shallow one. Formation of bars contineousley division of flow into multiple directions Braided channel.

Effects of decrease in bed load: This change can come along in a number of ways:

Reforestationof an abandoned farmland.

Building of dam, trapping sediment in the upstream reservoir.

Due to the decrease of the bed load a channel preciousley graded is no longer in equilibrium. As result: [Scour of stream trenching into th ealluvium and lowering of the stream profile] Degradation {also reffered to as channel trenching}. As result of this the channel takes a narrow cross section and developes steep, wall–like banks of alluvium. After this chnnel trenching, the former flooodplan is free from annual flooding and becomes a stream terrace.

Aftr degradation has taken place, the stream will normally attain a new and lower profile of equilibrium. Hwen the new equilibrium is established the stream will usually develop meanders and will shift laterally to form a new floodplain.

In many cases alternate cycles of aggradation and degradation produce a very complex series of terraces. These reflect the changing response of the stream to climatic changes.

Drainage pattern:

Definition: Distribution of stream courses and their spatial relationship to one other. Types:

1. Dendritic 5. Annular 2. Trellis 6. Parallel 3. Rectangular 7. Irregular 4. Radial

1. Dendritic:

Irregular branches of tributary streams in many directions at almost any angle (Usually less than or at right angle)

Most likely to be found upon horizontal rocks or in areas of massive igneous/metamorphic rocks.

Looks similar to that of the roots of trees.

2. Trellis

These are formed in places where the bands of rock resistant to weathering alternate with bands (of rock) that erode more rapidly.

The main streams frequently make nearly right angled bends to cross or pass between aligned ridges.

Primary tributary streams are usually at right angles to the main stream and are joined at right angles by the secondary tributaries whose courses are commonly paralleled to the main stream

This is a special variety of the rectangular pattern.

3. Rectangular :

Characterized by the bends in both the tributaries and the master streams

Generally right angle joints

4. Radial:

In the radial outward pattern the drainage line radiate outward from a common center. This center is located at an elevated location.

In the centripetal or radial inward type the streams flow into a common center from the circular basin walls.

5. Annular:

May be found around maturely disseeted domes which have alternating belts of strong and weak rocks encircling them

As breaching proceeds the initial radial drains completely disappear, influence of slope control ceases and concentric arrangements of streams (the annular pattern) on the least resistant formations will develop if other factors are negligible.

6. Parallel:

It consists of parallel master and tributary streams.

Pronounced regional slopes, parallel faults and parallel topographic features are the controlling factors in the formation of this type of drainage pattern.

7. Irregular:

Guess what!!

QUANTITATIVE ANALYSIS OF STREAM NETWORK

STREAM ORDER: Stream order is a measure of the position of a stream in the hierarchy of tributaries (Branches of stream)

PURPOSE OF MAKING STREAM ORDER:

To make comparison between different drainage basins.

To help making relationship between different aspects of drainage pattern of the same basin to be formulated as general laws.

To define certain useful properties of drainage basin in numerical terms.

HORTON’S SYSTEM OF STREAM RANKING: According to this system of stream ranking a stream which has no tributaries is a stream of 1st order. A stream which has tributaries of order 1, is a 2nd order stream. A stream which has 1st & 2nd order tributaries, is a stream of 3rd order.

BIFURACTION RATIO: The ratio between (Mean ratio) the number of streams of one order to the number of streams of next higher order is a constant and is called bifurcation ratio (B.R.).

For the stream network shown above:

Stream order Number of streams B.R. Average B.R.

1st 18 18/6=3 6/3=2 3/1=3

3 + 2 + 3

3

=8/3 = 2.667 2nd 16

3rd 3

4th 1

LENGTH RATIO (L.R.): The ratio between the mean lengths of stream of an order to the mean length of streams of the next lower order is a constant and is called length ratio (L.R.)

Stream order Mean length (miles) L.R. Average L.R.

1st 5.3 24.8/5.3=4.7 70.2/24.8=2.83 150.5/70.2=2.14

4.7 + 2.83 + 2.14

3

= 3.218 2nd 24.8

3rd 70.2

4th 150.5

CONSTANT OF CHANNEL MAINTENANCE: It is the drainage area required to be sustained by unit length of the channel. Length of channel (L) is given by the empirical formula: 𝐿 = 1.4 𝐴 𝑑

0.6 L= Mean length of the channel (mi), 𝐴𝑑= the area of drainage basin (𝑚𝑖2)

Drainage Density:

Drainage density = ∑ 𝐿𝑒𝑛𝑔𝑡ℎ

∑ 𝐴𝑟𝑒𝑎𝑑 =

𝐿

𝐴𝑑 ; Unit is ‘1/mile’

Length of overland flow: Length of overland flow= 1

2 X

1

𝐷𝑟𝑎𝑖𝑛𝑎𝑔𝑒 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 =

∑ 𝐴𝑑

2 ∑ 𝐿 ; Unit is mile

Stream Frequency: Stream frequency =𝑁𝑜.𝑜𝑓 𝑠𝑡𝑟𝑒𝑎𝑚𝑠 𝑖𝑛 𝑎 𝑛𝑒𝑡𝑤𝑜𝑟𝑘

𝑇𝑜𝑡𝑎𝑙 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑑𝑟𝑎𝑖𝑛𝑎𝑔𝑒 𝑏𝑎𝑠𝑖𝑛

Figure: changes in channel from of the San Juan River near Bluff, Utah, during the process the process of a flood. (Based on data of L.B. Leopold and T. Maddock, 1953, U.S.

LANDFORMS OF ALLUVIAL RIVER FLOODPLAINS: An alluvial river flows on a very gentle down valley gradient. The typical alluvial river has sinuous (snakelike) bends, called alluvial meanders, and occupies a floodplain. As we explained in the previous unit, the floodplain is a belt of flat land, present on one or both sides of the river channel, and subjected to inundation by overbank flooding annually or biennially. Before launching into an investigation of the hydrology of the river floods, it is helpful to know about the surface configuration and landforms of a typical alluvial river floodplain. A block diagram, in figure 29.1 shows these features in exaggerated form. An alluvial river flows on a thick accumulation of alluvial deposits constructed by the river itself in earlier stages of its activity. These sedimentary deposits, called alluvium, consists of clay, slit, sand, or gravel in various layered arrangements. The floodplain is bounded on either side by rising slopes, called bluffs. Dominating the floodplain are the meandering river channel itself and also the abandoned reaches of former channels. An air photograph, figure 29.2 shows these feature nicely. Meanders develop narrow necks, which are cut through, shortening the river course and leaving a meander loop abandoned. This event is called a cutoff. It is quickly followed by deposition of slit and sand across the ends of the abandoned channel, producing an oxbow lake. The oxbow lake gradually filled with fine sediment brought in during high floods and with organic matter produced by aquatic plants. Eventually the oxbows are converted into swamps, but they retain their identity indefinitely. During periods of overbank flooding, when the entire floodplain is inundated, water spreads from the main channel over adjacent floodplain deposits. As the current rapidly slackens, sand and silt are deposited in a zone adjacent to the channel. The result is an accumulation known as a natural levee. Between the levees and the bluffs is lower ground, the backswamp. Because deposition is heavier closest to the channel and decreases away from the channel, the levee surface slopes away from the channel. Figure 29.3 is a profile across a river channel and its flanking levees. Figure 2934 shows a river in flood. Notice that the higher ground of the natural levees is revealed by a line of trees on either side of the channel.

Figure 29.1: Floodplain landforms of an alluvial river.

Figure 32.5: Stages in stream trenching and terrace formation. (A) Aggradation by a braided stream has partly filled a valley with alluvium. (B) Trenching leaves a wide alluvial terrace (C) The graded stream forms a new floodplain by undercutting the terrace.

Effects of basin characteristics on the flood hydrograph: (a) Relationship of slope to peak discharge; (b) Relationship of hydraulic roughness to runoff. (c) Relationship of storage to runoff; (d) Relationship of drainage density to runoff; (e) relationship of channel length to runoff.

Figure 8.1.5 Effects of storm shape, size and movement on surface runoff. (a) Effect of time variation of rainfall intensity on the surface runoff; (b) effect of storm size on surface runoff; (c) effect of storm movement on surface runoff.

Figure 28.7 Schematic hydrograph showing effect of urbanization as reducing lag time and increasing peak discharge. Points CMP and CMR are centers of mass of rainfall and runoff.

MINERALS

Mineral: Mineral is the basic building blocks of rocks and solids.it can be defined as

1. Naturally occurring crystalline. 2. Inorganic substance with 3. A definite chemical composition and physical properties.

Mineral groups: Minerals are grouped according to the anion, or complex anion of their composition. The important mineral groups are presented in the following table. Notice that the suffix “ate” indicates that the anion is a complex anion that included oxygen. The two most important mineral groups by abundance in rocks are the carbonates (𝐶𝑂3) and the silicates (𝑆𝑖𝑂4)

Element Minerals

Silicates [elements+ ( 𝑆𝑖𝑂4)4−]

Oxides [elements +O]

Sulfides [elements +S]

Carbonates [elements + (𝐶𝑂3)2−]

Sulfates [elements + ( 𝑆𝑂4)2−]

Halides [elements + Cr, r, 𝐵𝑟− or 𝐹−]

Copper Ferromagnesian Cassiterite Chalococite Clacite Anhydrite Halite

Diamond Augite Corundum Galena Dolomite Gypsum Sylvite

Gold Biolite Hemaite Pyrite Magne site

Graphite Hornblende Ice Sphalerite

Platinum Olivine Magnetite

Silver Non Ferromagnesian

Sulfur Feldspars

Orthoclase

Plagioclase

Albite

Anorthlite

Muscovite

Quartz

Difference between Minerals and Rocks:

Minerals Rocks

Pure (made of same substances) More than one mineral

Some have crystals No single crystals

Usually pretty Not usually as pretty

Usually have a shape No definite shape

Color is usually same Color is not the same

No fossil Some have fossils

Physical properties of Minerals:

1. Crystal form 2. Cleavage 3. Striatior 4. Hardness 5. Specific gravity 6. Color 7. Streak 8. Fracture 9. Luster 10. Magnetism 11. Electrical properties.

Cleavage:

Cleavage is a directional property.

It is the tendency of a mineral to break in certain preferred direction along smooth plane surfaces.

It is a direction of weakness.

Minerals tend to break along planes parallel to this direction.

This weakness may be due to a weaker type of bonding.

Crystal form: Every mineral has a characteristic crystal form, which is the external shape produced by its crystal structure.

Striations: A few common minerals have parallel threadlike lines or narrow bands across their crystal faces cleavage surface. Example: Quartz.

Specific gravity: Every mineral has an average mass per unit volume. Most rock- forming minerals have a specific gravity of around 2.5 to 3.

Color:

Different minerals have different colors and are very sensitive to impurities. So color is not a

reliable property in identifications.

Containing IRON ions: - Dark colored (Dark Gray, Deep Red)

Containing aluminum: - Light colored (Purple, Deep Red)

Hardness:

Hardness is the measure of the resistance that a smooth surface of a material offers to

bring scratches

It is governed by the internal atomic arrangements of mineral elements.

If the binding force between atoms increases hardness of atom is also increased.

Hardness scale

Scale Mineral Remarks

01 Tale Softest

02 Gypsum

03 Calcite

04 Fluorite

05 Apatite

06 Orthoclase

07 Quartz

08 Topaz

09 Corundum

10 Diamond Hardest

Apparatus Hardness

Finger nail H<2.5

Copper penny 2.5<H<3

Steel Blended Knife 3<H<5.5

Quartz 5.5<H<7

Diamond 7<H

Streak:

It is the color of the minerals in finely powdered form

It is more characteristics than color and widely used for identification of minerals.

Fracture:

Whereas cleavages occur only in some gems, and within those, only in certain directions,

fracture can, and do, occur in all gems, and in any direction. A fracture is a break which is

not along a cleavage plane. With sufficient fore, any gem will fracture, although some do so

more readily than others. The edges of fractures are not smooth like those of cleavages, but

they do tend to have one of several basic appearances.

Different types are as follows:

Luster: Luster is the way a mineral reflects light. The two main types of luster are metallic

and nonmetallic.

Minerals

Silicates (Contains Si-0 tetrahedron) Non-Silicate

Ferromagnesian Non-Ferromagnesian

1. Si-0 tetrahedron is joined by ions of Fe/Mg 1. Do not contain Fe/Mg

2. Very dark / black 2. Light color.

3. High specific gravity 3. Relatively low specific gravity

4. Hardness relatively high. 4. Harness relatively low.

Example: Olivine, Augite, Biotite. Example: Quark, Feldspar, Muscovite.

Structure of minerals:

Difference between Mineral and Mineraloid

Mineral Mineraloid

Mineral is a naturally occurring crystalline, inorganic substance with a definite chemical compositions and physical properties.

The natural substance, which yield no definite chemical composition or crystalline structure.

Formed under high pressure and temperature.

Formed under low pressure and temperature.

Either element or compound. Amorphous substance may absorb other elements.

Example: Quartz, Augite. Example: Opal, Limonite.

Families of Minerals

Name of the family Characterized by Example

Pyroxene family (Large, complex, Group)

Single chain tetrahedron Augite

Amphibole family (Large, complex, Group)

Double chain tetrahedron Hornblende

Mica Sheet tetrahedron Biotite, Muscovite

Feldspar Framework tetrahedron Orthoclase, Plagioclase.

Feldspars:

Feldspars are most abundant rock forming silicates. They are characterized by framework

tetrahedron.

‘Feldspars’ comes from the German language. ‘Feld’ means field and ‘spath’ is a term used

by minerals for various nonmetallic minerals. So ‘Feldspars’ refers that field minerals or

minerals found in any field. Feldspars make up nearly 54% of the minerals of the earth crust.

There are two types of Feldspars:

1. Orthoclase (Potassium feldspar).

2. Plagioclase (Calcium feldspar).

Subject Orthoclase Plagioclase

Cleavage Orthoclase feldspars have cleavage planes that intersect at 900

Plagioclase feldspars have cleavage planes that intersect at 860

Electrical unbalance correction

Aluminum replaces silicon in every fourth tetrahedron and K+ correct the electrical unbalance.

In Albite (correction by na+): Aluminum replaces silicon in very fourth tetrahedron. In Anorthite (correction by ca++): Aluminum replaces silicon in every second tetrahedron.

Color White, Gray or pinkish Colorless, White, Blue, Black.

Specific gravity 2.57 Albite- 2.62 Anorthite-2.76

Formula K(𝐴𝑙𝑆𝑖3𝑂8) Albite-Na(𝐴𝑙𝑆𝑖3𝑂8) Anorthite- Ca(𝐴𝑙𝑆𝑖3𝑂8)

Feldspars- At a glance

Diagnostic ion

Name Specific Gravity

Symbol Formula Color

𝐾+ Orthoclase (Potassium feldspar)

2.57 Or K(𝐴𝑙𝑆𝑖3𝑂8) White, Gray, Pinkish

𝑁𝑎+ Albite (Sodium Plagioclasis)

2.62 Ab Na(𝐴𝑙𝑆𝑖3𝑂8) White, Gray, Green

𝐶𝑎++ Anorthite (Calcium Plagioclase)

2.76 An Ca(𝐴𝑙𝑆𝑖3𝑂8) White, Gray, Green

Significance

a) Orthoclase: Greek Orthos - Straight

Klasis - A breaking.

Orthoclase (straight breaking) signifies that these have cleavage planes interseeting at 900

b) Plagioclase: Greek Plagios – Oblique

Klasis - A breaking.

Plagioclasis (Oblique breaking) signifies that these have cleavage planes interseeting at 860

Question: When 𝐴𝑙3+substitutes for some 𝑆𝑖4+ ions in the silicate minerals, how is electrical

neutrality maintained. Give a specific example.

Ans.: In case of orthoclase feldspar plagioclase feldspar 𝐴𝑙3+ substitutes 𝑆𝑖4+ ions.

Orthoclase: 𝐴𝑙3+ replaces 𝑆𝑖4+ in every fourth tetrahedron.

Plagioclase:

1. Albite: 𝐴𝑙3+ replaces 𝑆𝑖4+ in every fourth tetrahedron.

2. Anorthite: 𝐴𝑙3+ replaces 𝑆𝑖4+ in every second tetrahedron.

As aluminum Charge is ‘+3’ & Silicon charge is ‘+4’ so, when aluminum replaces silicon then

an electric unbalance condition is occurred as Al & Si have not homogenous charge. But a

mineral must be in stable position by compemating the next charge. A correction is

introduced.

1. Orthoclase correction: Diagnostic ion is 𝐾+; Formula K(𝐴𝑙𝑆𝑖3𝑂8).

2. Albite correction: Diagnostic ion is 𝑁𝑎+; Formula Na(𝐴𝑙𝑆𝑖3𝑂8).

3. Albite correction: Diagnostic ion is 𝐶𝑎++; Formula Ca(𝐴𝑙𝑆𝑖3𝑂8).

Non silicate minerals:

1. Oxide minerals:

Oxide minerals are formed by the direct union of an element with oxygen.

Relatively simple than silicate minerals.

Oxide minerals are harder than other non-silicate minerals.

Common oxide minerals are: Ice (𝐻2𝑂); Corundum (𝐴𝑙2𝑂8); Hematite (𝐹𝑒2𝑂3).

2. Sulfide minerals: Sulfide minerals are formed by the direct union of an element with

sulfur. Common sulfate minerals are Pypite (𝐹𝑒𝑆2); Galena (PbS).

3. Carbonate minerals: Carbonate minerals are formed by the direct union of an element

with a complex ion 𝐶𝑂3. Common carbonate minerals are Calcite (𝐶𝑎𝐶𝑂3); Dolomite

CaMg(𝐶𝑂3)2.

4. Sulfate minerals: Sulfate minerals are formed by the direct union of an element with a

complex ion 𝑆𝑂42−. Common sulfate minerals are Gypsum (Ca𝑆𝑂4). 2𝐻2𝑂.

5. Halide minerals: Halide minerals are formed by the direct union of an element with the

halogen elements. Common halide minerals are halite (NaCl); Fluorite (Ca𝐹2).

Difference between Halide and Mineraloid

Halide

It is one kind of mineral. So it has definite chemical composition & crystal structure.

The Mineraloid substances have no definite chemical composition & have no crystal structure.

Halide must contain halogen( Cl, Br, I, F) Does not contain halogen.

Formed comparatively at high temperature and pressure

Formed at low temperature and pressure

Compound Amorphous Substance may absorb other elements

Example: Halide, Flurite. Example: Opal, Limonite.

IGNEOUS ROCK

Geothermal gradient: The increase in temperature with depth is called geothermal gradient.

Geothermal gradient=∆ 𝑇𝑒𝑚𝑝𝑎𝑟𝑎𝑡𝑢𝑟𝑒

∆𝐷𝑒𝑝𝑡ℎ

Generally rise in temperature is 100 c/km to 500 c/km. Average 300 c/km

Heat flow is the product of temperature, gradient and the thermal conductivity of earth’s

material.

Igneous rock: Igneous rocks are formed by the solidification of magma. A magma is a natural,

hot melt composed of a mutual solutions of rock forming materials (mainly silicates) and some

volatiles (mainly stream) that are held in solution by pressure. Magma may erupt from vents

time or it may trapped inside the crust, where it slowly cools and solidifies.

Igneous rocks compose of the 95% of the outermost 10 km of the earth.

Masses of igneous rocks: when magma within the crust losses its mobility, stops activity; it

solidifies in place, forming igneous rock masses of varying shapes and sizes.

Plutons: all igneous rock masses that where formed when magma solidified within the earth’s

crust are called plutons. Plutons are classified according to their size, shape and surrounding

rocks.

Concordant: When rocks have a definite layering and the magma with boundaries parallel to

the layer is called concordant.

Discordant: Magma with boundaries cutting across the layering is called discordant.

Tabular Pluton: When pluton is thin relative to its other dimension is called a tabular pluton.

Sill: A tabular concordant pluton is called sill. It may be horizontal, inclined, and vertical. Its

surface may be smooth, rough. It may be contain fragments of rock.

Lapoliths: Tabular concordant plutons. Spoon shaped. Concave roof (sagging downward),

Convex floor. Most Lapoliths are composed of rock that has been differentiated into

alternating layers of dark and light mineral.

Dikes: Tabular discordant pluton. Dikes originated when magma forced its way through the

fracture of adjacent rock.

1. Ring dike:

i) As magma factors its way upward, it sometimes pushes out a cylindrical section of the

crust.

ii) By course of time it generates circular elliptical shape.

2. Cone sheets dike: These dikes originated in fractures that outline an inverted cone with the

apex pointing down into the former magma source.

3. Dike swarm: when dikes are found approximately parallel groups.

Massive pluton: The plutons other than the tabular shape are called massive plutons.

Laccoliths: massive concordant pluton. When magma pushes overlying rocks into a dome then

lacoliths is formed.

Batholiths:

- Massive discordant pluton.

- Surface exposer more than 100𝑘𝑚2.

- Increase in size as it extends downward.

- Batholiths are located in mountain ranges.

- Usually run parallel to the axes of mountain ranges.

- Batholiths have been intruded across the folds.

- Batholiths have irregular dome shaped roofs.

- Are composed primarily of granite.

- Contains a great volume of rock.

Question: How have igneous rocks formed?

Answer: igneous rocks are formed from the solidification of magma. Magma solidifies through

the process of crystallization. Magma is natural of melt composed of a mutual solution of rock

forming minerals and some volatiles (mainly steam) that are held by pressure. Magma may

erupt from vents time to time or it may trap inside the crust, where it slowly cools and

solidified. Magma extruded as lava at the sources, cools and solidifies to from igneous rocks.

Some definitions:

Pyroclastic debris: When solidified pieces of magma are blow out, they are pyroclastic debris.

Tuff: volcanic ash that has hardened into rock is tuff.

Volcanic breccias: When many relatively large angular blocks of congealed lava are embedded

in a mass of ash and then hardened to rock is called volcanic breaches.

Volcanic conglomerate: it rounded fragments of congealed lava pieces are embedded in a

mass of ash and then hardened to rock, is called volcanic conglomerate

Crystallization of magma: (Bowen’s reaction principle)

Introduction:

- Magma is a solution of element.

- But it does not crystalize in the ordinary way.

- Magma of a given composition may be able to crystalize in a number of rocks.

Dependable factor:

Bower proposed that,

a) The differences in end product depends upon

i) Rate at which magma cools.

ii) Rate of crystallization.

Whether the early formed minerals remain in or settle out from the remaining liquid during

crystallization.

b) The first formed minerals undergo continues modification with the liquid remaining after

they crystalized in a process called reaction.

Reaction series:

When one mineral develops from magma then it will be converted into new minerals by

reacting with the remaining liquid upon further cooling.

The reaction series is of two types:

1) Continuous series

2) Discontinuous series.

Continuous reaction series:

- Some early formed minerals are converted into new minerals.

- Compositions changes.

- Crystalline structure remains same.

- Feldspars constitutes continuous series.

Discontinuous series:

- Some early formed minerals are converted into new minerals.

- Compositions changes.

- Crystalline structure changes.

- Ferromagnesian minerals constitute discontinuous series.

Fractionation:

The procedure of setting out of minerals produced early from the cooling of magma called

fractionation.

Explanation of crystallization of magma in terms of fractionation:

1) Rock forming minerals Discontinuous ferromagnesian series

Continuous plagioclase series.

2) As magma cools Olivine, Anorthite

3) When no minerals settle out𝑆𝑜𝑙𝑖𝑑𝑖𝑓𝑦

𝑜𝑟 𝑚𝑒𝑙𝑡 Basalt or Gabbros

4) When some minerals settle out 𝐹𝑟𝑎𝑐𝑡𝑖𝑜𝑛𝑎𝑡𝑖𝑜𝑛 The Remaining mineral react with melt.

Effect of rate of crystallization:

- The rate of crystallization of magma influences the extent to which fractionation and

reaction take places.

- When magma cools rapidly then there is no time for the minerals to react with the

remaining melt.

- The rate of crystallization increase with depth.

Texture of igneous rocks:

Texture is a physical characteristic of all rocks. The term texture refers to the general

appearance of rocks. Such as -

The size

The shape

The arrangement of interlocking mineral grains.

The texture depends mainly upon –

a) Rate of cooling.

b) Viscosity of magma.

c) The uniformity of cooling.

Types of texture:

A) Granular texture

B) Aphanitic texture

C) Glassy texture

D) Porphyritic texture.

A) Granular texture:

- Large grains on crystals.

- Grains can be seen by unaided eye.

- The large grains are developed by the slow rate of cooling magma.

- The other name is ‘Phaneritic’ texture.

Controlling factor for development of granular texture:

a) The slow rate of cooling of magma develops the coarse grain.

b) The low viscosity magma (that is thin, watery & flows readily) may be cooled rapidly but

due to the quick mobility, ions of magma can move easily and quickly combined with rock

forming minerals.

Example: Granite, Gabbro.

B) Aphanitic texture:

- Small crystal grains.

- Grains are too small to identify without magnification.

- Results of moderately rapid cooling.

Controlling factor for development of Aphanitic texture: The rapid cooling rate of magma is

responsible to develop finer grain, the result is Aphanitic texture.

C) Glassy texture:

- Non crystalline.

- Amorphous, compact.

- Disorganized ions.

- Result from the sudden ejection of magma.

- Frozen liquid by changing temperature rapidly.

Controlling factor for development of glassy texture:

Ejection of magma

Lava on earth surface

Cooling very rapidly

So, no time to form grain

Glassy

D) Porphyritic texture:

- Mixed texture.

- Crystal as well as glasses are present.

- Result from two different rates of cooling.

Controlling factor for development of porphyritic texture:

At first, slow rate of cooling of magma develops coarse grains of minerals. [Phenocrysts]

Then condition of rapid cooling has frozen the coarse grains so that it develops finer grains of

minerals. [Porphyritic texture]

Note: ‘Porphyry’ is a Greek word meaning ‘purple’ was originally applied to rocks containing

phenocrysts in a dark red or purple groundmass.

Types of igneous rocks:

- Light colored or Sialic.

- Dark colored or Siamatic.

- Intermediate or Mixed.

SOME IGNEOUS ROCKS

Rock Type Texture Composition Remark

Granite Light colored, Igneous rock,

static

Granular or Phanitic

2 parts orthoclase feldspar+ 1 part quartz+1 part plagioclase

feldspar + small amount of ferromagnesian [Granite]

(50% orthoclase+25% plagioclase+25% quartz)

Intrusive

Rhyolite Light colored, static

Aphanitic 2 parts orthoclase feldspar+ 1 part quartz+1 part plagioclase

feldspar + small amount of ferromagnesian [Rhyolite]

(50% orthoclase+25% plagioclase+25% quartz)

Extrusive

Obsidian Light colored, Igneous rock

Glassy (50% orthoclase+15% plagioclase+25% quartz+10%

ferromagnesian)

Extrusive

Gabbro Dark colored, Igneous rock,

siamatic

Granular or Phanitic

1 part ferromagnesian+1 part plagioclase feldspar

(50% plagioclase+50% ferromagnesian)

Intrusive

Basalt Dark colored, Igneous rock

Aphanitic 1 part ferromagnesian+1 part plagioclase feldspar

(50% plagioclase+50% ferromagnesian)

Extrusive

Periodotite Dark colored, Igneous rock

Granular 25% plagioclase+75% ferromagnesian

Andesite Intermediate rock, mixed

Aphanitic 70% plagioclase+30% ferromagnesian feldspar

Diorite Intermediate rock, mixed

Granular 70% plagioclase+30% ferromagnesian feldspar

Dlinite 100% ferromagnesians

SEDIMENTARY ROCKS

Sedimentary rocks: Sedimentary comes from the Latin word ‘Sedimentum’ means setting.

Stratification is the single most characteristic (layering) feature of sedimentary rocks.

Amounts of sediments: 75% rocks exposed at earth’s surface are sedimentary + metamorphic

rocks.

Source ton/ year

Rivers 1010

Glaciers 108~109

Wind 108

Extraterrestrial 0.03 to 0.3

In case of delta of Bangladesh Rivers carry sediments 2 billion tons per year out of 10 billion

tons per year. Some example of delta’s are:

1. Ganges, Brahmaputra, Jamuna, Meghan Delta.

2. Nile Delta.

3. Mississippi Delta.

In Dhaka city sediments layer thickness is 12~14 km.

Formation of sedimentary rocks:

Sedimentary rocks

Detrital Non Detrital or chemical

Inorganic Biochemical or organic

A) Detrital:

Deposits produced by “Mechanical Means” Erosion & weathering. 𝐸𝑟𝑜𝑠𝑖𝑜𝑛

𝑊𝑒𝑎𝑡ℎ𝑒𝑟𝑖𝑛𝑔 of rocks

𝐸𝑟𝑜𝑑𝑒𝑑 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙

𝑊𝑒𝑎𝑡ℎ𝑒𝑟𝑒𝑑 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 Deposition

Sedimentary rocks formed by detrital way are called detrital sedimentary rocks.

Example:

Granite weathering Quartz grain free from granite transportation and sedimentation

Setting as bed

Sandstone (Sedimentary rock)

Particle size/ Composition Rock name

Larger particles Conglomerate

Sand Snadstone

Silt Siltstone

Clay Mudstone and shale

B) Chemical or non-detrital:

Deposits are produced by the chemical process.

1) Directly process (Inorganic):

Salt body of water evaporation Salt left behind Deposition of salt by inorganic chemical process

2) Indirect process (biochemical):

- Corals extract 𝐶𝑎𝐶𝑂3 from sea water and use it to build up skeletons of calcite.

-When animals die, their skeletons are collected as biochemical deposits and subsequently

from biochemical rock in this case limestone.

Sedimentary rocks represent origin of environment:

(a) Marine: Rocks containing fossils of sea animals.

(b) Fluvail: Rocks forming by deposits laid down by rivers.

(c) Eolian: Rock forming by wind deposited material.

(d) Lacustrine: Rocks formed from lake deposits.

Marine Marine

Fluvail River

Eolian Wind

Lacustrine Lake

Difference between Detrital and Chemical ways:

Detrital Chemical

Deposits produced by mechanical means. Deposits produced by chemical process.

Deposits through erosion or weathering. Deposited by precipitation.

Sedimentation:

- The general process by which rock forming material is laid down is called

sedimentation.

- When the agent of transportation of detrital material has less energy to transport the

material then it is deposited.

Example:

Stream flows with Transportation of velocity decreases All particles can’t be

transported Deposited on bed.

Chemical: By participation materials that has been carried in solution converted into new

solid and separated from the liquid solvent.

Question: Describe the process by which clay material are produced from existing rocks.

Answer:

- Due to erosion or weathering deposits may be produced.

- These deposits are then transported by agents like, wind, stream etc.

- Then these transported materials existing from rocks may produce clay on the way of

sedimentation process.

Process-01:

Step-01: 𝐻2𝑂 reacts with 𝐶𝑂2 and produce 𝐻+.

𝐻2𝑂+𝐶𝑂2 𝐻2𝐶𝑂3 𝐻++ (𝐻𝐶𝑂3)−

Step-02: Now this existing 𝐻+reacts with feldspar, which is the most common minerals found

on earth.

2(𝐾𝐴𝑙𝑆𝑖3𝑂8) + 2𝐻+ + 𝐻2𝑂 𝐴𝑙2𝑆𝑖2𝑂5(𝑂𝐻)4 + 2𝐾+ + 4𝑆𝑖𝑂2 (quartz/sand).

Step-03: Due to the velocity of the water body, clay particles go to the bank of water body

and sand falls down due to its weight.

Process-02:

Step-01: Roots of trees have a large amount of ions of hydrogen (𝐻+).

Step-02: This 𝐻+ react with feldspar resulting the production of clay.

So, Feldspar + 𝐻+ 𝑯𝒚𝒅𝒓𝒂𝒕𝒊𝒐𝒏

𝑯𝟐𝑶 Clay + Quartz

Principle constituents of sedimentary rocks:

Three most common minerals are:

1) Clay

2) Quartz

3) Calcite

1) Clay:

- Develop from the weathering of silicate, particularly the feldspars.

- These clays may be subsequently incorporated into the sedimentary rocks.

- Kaolinite and illite are the most common clays in sedimentary rocks.

- Montmorillonite is rare clay.

2) Quartz:

- Formed from the mechanical and chemical weathering of the igneous rock specially

granite.

- Detrial forms of silica.

- Acts as cementing material in coarse grain sedimentary rocks.

- Predominant constituents of sandstone.

3) Calcite:

- Chief constituents of limestone.

- Most common cementing material in coarse grained sedimentary rocks.

- Formed by detrital and non-detrital processes.

Other minerals:

Dolomite, Feldspar, NaCl, Gypsum, Iron, Organic matter.

Silica may also be precipitated in other forms:

1) Opal: a) Softer than quartz.

b) No true crystal structure.

2) Flint: a) Granular in texture.

b) Dark in color.

3) Chert: Light colored flint.

4) Jesper: Granular

Texture of sedimentary rocks:

1) Clastic texture.

2) Nonclastic texture.

1) Classic texture:

- Rock formed from deposits of minerals or, rock fragments are clastic texture.

- The size and he shape of the original particles have a different influence on the

resulting texture.

- Chemical sedimentary rocks also show clastic texture.

2) Nonclastic texture:

- Grains are interlocked.

- Have crystalline structure.

- These rocks have somewhat the same the same appearance as igneous rocks with

crystalline texture.

Depending on size of crystals texture are divided into three types:

(1) Fine grained.

(2) Medium grained.

(3) Coarse grained.

Lithification: The process by which the unconsolidated rock forming materials convert

into consolidated rocks.

Unconsolidated material Lithification Consolidated rocks.

Process of lithification:

a) Cementation.

b) Compaction and desiccation.

c) Crystallization.

d) Digenesis.

a) Cementation:

- Pores of consolidated deposits are filled by cementious material.

- The most common cementing materials are calcite, dolomite, quartz.

b) Compaction and desiccation:

Pressure develops on sediments Compaction Pore space between adjacent grains reduce.

In desiccation the water that originally filled the pore spaces of water laid clay and silt deposits

is forced out. Sometimes this is the direct result of compaction but desiccation also takes

place when a deposit is simply exposed to the air and the water evaporates.

c) Crystallization:

Weathering/erosion rock forming material Transportation

Sedimentation crystallization Harden deposit.

d) Digenesis:

Deposition of rock change Modified rock forming material.

This modification process contains the change of physically, chemically and biologically.

As example:

1) Bacterial decomposition of organic matter.

2) Removal of soluble materials such as 𝐶𝑎𝐶𝑂3 may dissolve in sea water in deep sea

sediments.

SOME SEDIMENTARY ROCKS

Name Origin or

Type

Texture Formation Size of Particle

Other Form

Mudstone Detrital Clastic Formed by fine clay and silt which are very

difficult to examine visually.

Less than 1

16mm. dia

1)Mudstone 2)Pelites 3)Shales

Sandstone Detrital Clastic Formed by the consolidation of grains

of sand.

1

16~2 mm

dia

1) Ortho Quartizite

2)

Conglomerate Detrital Clastic Formed by rounded fragments only.

2-4 mm dia 1) Tillite 2)Breccia

Limestone Non Detrital

Clastic or Non- Clastic

By 𝐶𝑎𝐶𝑂3, i.e, Mineral Calcite mix with other

Calcite deposits

------ 1)Dripstone 2)Tufa

Dolomite Non Critical

Clastic or Non- Clastic

When mineral ‘Dolomite’

𝐶𝑎𝑀𝑔(𝐶𝑂3)2in large concentration then

rock will form

------ ------

Evaporates Non Detrital

Clastic or Non- Clastic

By evaporation of liquid, the minerals are exposed and then form

rock

------ 1) Rock Salt 2)Anhydrite

Chalk Non Detrital

Clastic or Non- Clastic

Biochemically Calcite are mixed with calcite

deposite and then form chalk

------ ------

Difference between Limestone and Chalk:

Limestone Chalk

Mineral Calcite + Other calcite (organic or inorganic) = Limestone

Biochemical Calcite+ Other Calcite (Skeleton form of plants and animals) = Chalk

Some features of sedimentary Rocks

1. Bedding:

- The beds or layers of sedimentary rocks are separated by bedding planes, along which

the rocks tends separate.

- Each bedding planes marks the termination of one deposit and beginning of another.

- Bedding planes are usually horizontal.

Parallel Bedding: When bedding planes are parallel.

Laminated bedding: Closely spaced parallel bedding planes.

Cross Bedding: Bedding planes laid down at an angle with horizontal.

2. Ripple Mark:

-Little waves of sand that commonly develop on the surface of sand dune, along a beach

or on the bottom of a stream.

4. Nodule:

-An irregular knobby surfaced body of mineral matter that differs in composition from the

sedimentary rocks in which it has formed.

5. Concentration:

-A local concentration of cementing material that has lithified a deposit into sedimentary

rocks.

6. Geodes:

-Roughly spherical hollow structures upto 30 cm or move in diameter which is more eye

catching Nodule and concentration.

METAMORPHIC ROCK Metamorphism: Some sedimentary and igneous rocks have changed with the change of

environment. This process of modification is called metamorphism.

Metamorphism occurs within the earth’s crust below the zone of weathering and

cementation above the zone of re-melting.

Agents of Metamorphism:

1. Heat:

a) Most essential agent.

b) Thermal gradient (∆𝑡

∆𝑥) 100C to 500C/km.

c) Heat accelerates most chemical reaction.

2. Pressure:

a) Pressure may rearrange the positions of minerals by reducing the pore.

b) Produce a closer atomic packing.

c) Recrystallization.

d) Formation of new minerals.

e) Gradient (∆𝑝

∆𝑥) 200~300 bar/km.

3. Chemically active fluids:

Releasing of magma Solidification of magma some solution go down that Percolate

Affect to surrounding rocks Chemical reactions and produce new minerals

Metamorphisms

Types of metamorphism:

1) Contact metamorphism

2) Regional metamorphism.

1) Contact Metamorphism:

Intrusion of magma into earth crust Alters/Change characteristics of surrounding rocks.

This alteration of rocks at near of magma is called contact metamorphism.

Zone: Aureoles/Halos

Factors:

i) Temparature

ii) Composition and intruding mass.

iii) Properties of intruded rocks.

Temparature: 3000C to 8000C.

Pressure: 100 to 3000 atmosphere or bars.

Contact metamorphic Minerals:

a) Impure limestone + Quartz = Wollastone +𝐶𝑂2.

b) Impure dolomite+ quartz= Diopside+𝐶𝑂2.

c) Aluminum In clay Corundum or Garnet.

d) Carbon materials temperature Graphite.

2) Regional Metamorphism:

Regional metamorphism is formed over large areas.

May involve thousands of square km. of rock, thousands of meters thick.

Mew minerals will form.

Temperature and pressure differency will result in different metamorphism (Hogh,

Low, Medium grade).

High grade metamorphism: Intense temperature and pressure on rock and change.

Low grade metamorphism: Least change of rock.

Medium grade metamorphism: It lies between high and low metamorphism.

Regional metamorphism minerals:

Mineral Composition Cleavage Hardness Color Streak Formula

Kyanite Independent 𝑆𝑖𝑂4

Tetrahardon with (+ve) Al

ions

1 direction 5~6 Blue, White, Gray, Green

Colorless 𝐴𝑙2𝑆𝑖𝑂5 (blade like

blue crystals)

Sillimanite Independent 𝑆𝑖𝑂4

Tetrahardon with (+ve) Al

ions

1 direction 6~7 Brown, Green, White

Colorless 𝐴𝑙2𝑆𝑖𝑂5 (long

slender crystals)

Andalusite Independent 𝑆𝑖𝑂4

Tetrahardon with (+ve) Al

ions

Not prominent

7.5 Red, Brown

Colorless 𝐴𝑙2𝑆𝑖𝑂5 (coarse square prisms)

Garnet Al, Fe, Mg, Ca, Mn, Cr

No cleavage

6.5-7.5 Red, Brown

Colorless

Epidote Ca, Al, Fe 1direction 6-7 Pistachio Green

Colorless

Chlorite Ca, Al, Fe, Mg

1 direction 2-2.5 Green shade

Colorless

Staurolite Al or Fe ions No cleavage

7-7.5 Reddish Colorless

Regional metamorphic zones:

High grade Low grade Middle grade

-High temperature & pressure. –Least charge -Medium

-Intense change.

Identification of zones:

Zones are identified by certain diagnostic minerals called index minerals.

A= Andalusite

K= Keyanite

S= Sillimanite

Under regional metamorphism new minerals are developed with respond to increase in

temperature and pressure.

Increasing Zone Grade

Chlorite Low

Biolite Low

Garnet Middle

Staupolite Middle

Kyanite Middle

Metamorphism Sillimanite High

For minerals composed of 𝐴𝑙2𝑆𝑖𝑂5 :

1) Kyanite: Low temperature + Wide range of pressure

2) Andalusite: Moderate temperature + Low pressure

3) Sillimanite: High temperature+ Wide range of pressure.

Question: How index minerals indicate the process and condition of origin?

Regional Metamorphic Facies:

- A facies is the combination of minerals, rock or fossil features that represent the

environment in where the rock was formed.

- A metamorphic facies is the combination of minerals that reached in stable condition

udder a set of conditions.

- Each facies is named after a common metamorphic rock that belongs to it.

- Dividing the areas of curve into several zones.

- Typical mineral assemble are represent for metamorphism of a shale and a basalt.

Regional metamorphism Facies:

Facies Temperature/Pressure Shale Basalt

Zeolite 2000~3000c 2~3 Kbar

Illite, Chlorite, Quartz

Zeolites

Green Scist 3000~5000c 3~8 Kbar

Muscovite, Chlorite, Quartz

Albite, Chlorite, Epidole

Blue Scist 2000~4000c Above 5 Kbar

Muscovite, Chlorite, Quartz, Garnet

Glaucophane, quartz, lowsonite

Amphibolite 4500~7000c Above 3~8 Kbar

Muscovite, Chlorite, Quartz, Garnet, Biotite, Plagioclase

Amphibole, Plagioclase, Garnet

Granulite Above 6500c 3~12 Kbar

Quartz, Garnet, Biotite, Plagioclase

Calcic Pyroxene, plagioclase

Eclogite Above 3500c 7~10 Kbar

--------------- Sodic Pyroxene, Garnet

Question: Write the difference between Diagenesis and Metamorphism with example.

Answer:

Diagenesis:

Deposition of rock forming material/mineral change Modified rock.

This modification process contains the change of physically, chemically and biologically. It

occurs before any metamorphic changes.

As example:

1. Bacterial decomposition of organic matter.

2. Removal of soluble materials such as 𝐶𝑎𝐶𝑂3 may dissolve in sea water in deep sea

sediments.

Diagenesis may occur in zone of weathering and cementation.

Metamorphism:

Some sedimentary and igneous rocks have changed with the change of environment. This

process of modification is called metamorphism.

Metamorphism may occur with the earth’s crust below the weathering and cementation

zone. As example: Quartz Metamorphism Quartzite

Texture of metamorphic rocks: Rock subjected to heat and pressure during regional

metamorphism tend to be arranged in parallel layers of elongated grains. This type of

arrangement gives the rock a properly called foliation.

Texture Foliated

Unfoliated

EARTHQUAKE

Earthquake: Sudden movement of the crust of the earth is called earthquake.

Causes of earthquake:

- Slippage along a fault plane.

- Releasing strain energy.

- Volcanic eruption

- Landslide

Earthquake

Tectonic Volcanic

Large scale Small scale

Due to building up and release of strain energy May be due to volcanic eruption

May be due to strike and slip Localized

Liquefaction:

- It is the condition in which the soil changes temporarily from a solid to a liquid state.

- It is the most common phenomena where deposits are saturated i.e. along sea course and

shores of lakes and rivers.

- Occurs about 10 minutes after earthquake strikes a region.

- Underground sewerage, storage tanks, pipes and piles driven into the ground may float

up to the surface.

- Nearby structures may settle several meters into the ground

- Water and stand may be ejected into the air for several minutes.

Focus/Hypocenter:

- Source of given set of earthquake waves

- Point of faulting and first point of releasing of energy.

- Under the earth’s surface, generally within 100km.

Epicenter: Point on earth’s surface just above the focus.

Position: On earth’s surface.

Characteristics: It is not the most intensity shaken area. Because faulting plane is not

vertical exactly and rapture alone a considerable distance.

Earthquake Waves (Created by fault raptures)

Earthquake Waves

Body Wave Surface Wave

(Travel through interior mass) (Travel along surface)

P Wave S Wave Love Wave Rayleigh Wave

Body Waves

Travelling through the interior of the earth, body waves arrive before the surface waves

emitted by an earthquake. These waves are of a higher frequency than surface waves.

P Wave (Primary Wave)

- Longitudinal waves (As sound).

- Primary wave through which ground motion is transmitted.

- Fastest travelling wave (Velocity = 8km/sec).

- Particle moves parallel to the direction of propagation

- Continuous push and pull on the ground.

S Wave (Secondary Wave)

- Secondary wave.

- Transverse type.

- Particle moves at right angles to the direction of propagation.

- Travels only through materials that resists a change in shape.

- Velocity=3.25 km/sec.

Surface Waves

Travelling only through the crust, surface waves are of a lower frequency than body waves,

and are easily distinguished on a seismogram as a result. Though they arrive after body

waves, it is surface waves that are almost entirely responsible for the damage and

destruction associated with earthquakes. This damage and strength of the surface waves

are reduced in deeper earthquakes.

Love Wave

- Surface wave.

- Similar to S wave with no vertical displacement.

- Moves the ground from side to side parallel to the earth surface.

- Produces horizontal shaking.

Rayleigh Wave

- Surface wave.

- Disturbed materials move both horizontally and vertically in a vertical plane pointing

to a direction in which waves are travelling.

- Slower than love wave.

Measurement of Earthquake

Seismology: Seismology is the study of earthquakes and seismic waves that move through

and around the earth. A seismologist is a scientist who studies earthquakes and seismic

waves.

Earthquake is measured in two ways- 1) Magnitude and 2) Intensity.

Earthquake Magnitude:

- Richter scale of magnitude.

- Richter scale is based on the maximum amplitude of certain seismic waves at a

distance 100 km from epicenter.

- No indication about duration and frequency.

- Each higher whole number denotes a 10 fold increase in amplitude and 30 fold

increase in energy.

- Absolute value

Earthquake intensity

- It is the measure of the effects of earthquake on human beings, structures and earth

surface.

- No absolute value.

- Based on subjective observation.

- Modified Merealli Intensity method is used.

- 12 degree of intensity scale.

- Intensity of particular earthquake depends from place to place due to-

i) Distance from earthquake.

ii) Nature of ground.

Elastic rebound theory

The elastic rebound theory was the first theory to satisfactorily explain earthquakes.

Previously it was thought that ruptures of the surface were the result of strong

ground shaking.

According to this theory an earthquake is the result of the elastic rebound of

previously stored elastic strain energy in the rocks on either side of the fault.

The deformation builds at the rate of a few cm per year, over a time period of many

years.

When the accumulated strain is greater than the frictional strength of the rocks

earthquake occurs.

The blocks suddenly slip at a certain point. This point is known as the focus (or

hypocenter) of the earthquake.

One rupture is initiated it will travel at a high speed.

In great earthquakes, the slip, or offset of the blocks can be as large as 15m.

𝒎 = 𝐥𝐨𝐠(𝒂

𝑻) + 𝑩

m= Magnitude

A= Maximum trace motion

a= Maximum ground motion (microns=10−6m)

= A magnification of seismograph

B=correction factor that allows for the weakening of seismic waves with increasing distance

from the earthquake (found from table using distance)

T= Duration of one oscillation or period of seismic wave.

Earthquake magnitudes energies, effects and statistics

Characteristics effect of shallow shocks in

populated areas

Approximate Magnitude

Number of earthquake per year

Energy (ergs)

Damage nearly total ≥8.0 0.1-0.2 ≥1025 Great damage ≥7.4 4 ≥4X1024

Serious damage, rails bent.

7.0-7.3 15 0.04-0.2X1024

Considerable damage to the building

6.2-6.9 100 0.5-23X1021

Slight damage to the building

5.5-6.1 500 1-27X1019

Felt by all 4.9-5.4 1400 3.6-57X1017

Felt by many 4.3-4.8 4800 1.3-27X1016

Felt by some 3.5-4.2 30000 1.6-76X1015

Not felt but recorded 2.0-3.4 800000 4X1010X9X1013

Finding the epicenter

You have just figured out how far your seismograph is from the epicenter and how strong

the earthquake was, but you still don’t know where the earthquake occurred. This is where

the compass, the map, and the other seismograph records comes in.

Figure: The point where the three circles intersect is the epicenter of the earthquake. This

technique is called triangulation.

1. Check the scale on your map. It should look something like a piece of a ruler. All maps are

different. On your map, one centimeter could be equal to 100 kilometers or something like

that.

2. Figure out how long the distance to the epicenter (in cm) is on your map. For example, say

your map has a scale where one centimeter is equal to 100 kilometers. If the epicenter of the

earthquake is 215 kilometers away, that equals 2.15 centimeters on the map.

3. Using your compass, draw a circle with a radius equal to the number you came up with in

step #2 (the radius is the distance from the center of a circle to its edge). The center of the

circle will be the location of your seismograph.

4. Do the same thing for the distance to the epicenter that the other seismograms recorded

(with the location of those seismographs at the center of their circles). All of the circles should

overlap. The point where all of the circles overlap is the approximate epicenter of the

earthquake.

How to locate the epicenter?

Due to certain difference in wave velocity, the interval between the arrival of P and

S waves increases with the distance traveled by the waves.

For each S-P time interval there is associated a definite distance to the epicenter.

Knowing the distance ‘x’ of an earthquake from a given station, one can only say the

earthquake lies on a circle of radius ‘x’, centered on that station.

If one also knows the distances from two additional stations, the three circles

centered on 3 stations, intersect uniquely at the epicenter.

IX Ruinous -Heavy damage to buildings, ground cracks.

-General panic -Damage of masonry - Damage of foundation of frames structure -Underground pipes broken

6.6-7.0

X Disastrous -Most buildings destroyed, landslides. -Large landslide

7.1-7.3

XI Very Disastrous

-Railroads bent and pipelines beak -underground pipes completely out of service

7.4-8.1

XII Catastrophic -Total devastation -Objects thrown into air

>8.1

Modified Mercalli Scale

Advantages:

Provides the local information about ground shaking that is of most concern to

designers.

Disadvantages:

The MM scale, while being directly oriented to building effects, relies on a methodology

of subjective comparisons.

Its age: The listing of construction materials emphasizes masonry, and does not refer to

many modern methods of construction such as glass curtain walls, hung ceilings or precast

concrete.

Seismicity: Convergent Boundary

95% of total earthquake

Shallow, intermediate and deep focus

Mainly compressional force

Compressive force tend to strengthen rocks

Large amount of energy accumulated

High in magnitude

Low in frequency

Seismicity: Divergent Boundary

Narrow belt of shallow earthquake

Coincide with the crest of oceanic ridges.

Marks the boundaries between diverging plates

Earthquakes in this zone are:

*Less than 70km deep

*Small in magnitude

Appears as a nearly continuous line on maps

But there are two types of seismic boundaries that are distinguishable on the basis

of fault motion.

*Spreading centers:

Normal faulting

Intrusion of magmas

*Transform faults:

Not volcanic activities

Seismicity: Intraplate

Although most of the world’s seismicity occurs along plate boundaries, the

continental platforms do experience infrequent and scattered shallow focused

earthquake.

The ocean floors beyond the spreading centers are seismically inactive, expect for

isolated earthquakes associated with oceanic volcanoes.

To the east, the Tripura-Naga Orogenic belt is a highly faulted zone.

Along the borders of the Shilong massif occur a number of faults of which the Sylhet fault,

the Kopili fault, and the Dauki fault are worth mentioning.

Running in north-suth direction, there is the Jamuna fault.

To the north-east of the country the shilong plateau is separated from the sylhet plain by

east-west trending Dauki fault.

Five tectonic blocks: 1) Bogra fault zone; 2)Tripura fault zone; 3) Sub-Dauki fault zone;

4)Shillong plateau; 5)Assam fault zone.

During the last 150 year, 7 major earthquakes have affected Bangladesh.

They had Richter magnitude more than 7.

Only 2(1885 & 1912) had their epicenter within Bangladesh.

Zone-3:

Sylhet-Mymensingh is with the possible magnitude of 7 on Richter scale.

Zone-2:

Chittagong-Comilla-Dhaka and Tangail are with the possible magnitude of 6 on

Richter scale.

Zone-3:

Rest of the country.

GEOLOGY OF BANGLADESH

Physiography of Bangladesh

Quaternary sediments deposited mainly by the Ganges (Padma), Brahmaputra and Meghna

rivers and their numerous distributaries, cover about ¾ of Bangladesh. Bangladesh may be

subdivided in 24 physiographic sub-region and 54 units. (According to “Rashid-1997”).

The main sub-regions are:

1. Himalayan Piedmont Plain.

2. Flood plains of Tista, Old Brahmaputra, Jamuna, Ganges and Meghna rivers.

3. Barind Tract.

4. Madhupur Tract.

5. Foolhils of shilong Massif.

6. Haor Basin.

7. Tippera Surface.

8. Delta.

9. Chittagong Hill Tracts.

1. Himalayan Piedmont Plain [1]

Area: North-Western corner of Bangladesh, Greater Rangpur and Dinajpur.

Characteristics:

i) Covered by piedmont sand and gravels deposited by Mahananda and Karatoya Rivers and

their tributaries.

ii) Gentle slope.

iii) Average height 33m above MSL

2. Flood plains or rivers

a) Tista flood plain: [2, 3]

Area: Between Himalayan Piedmont plain and the right bank of Brahmaputra.

Characteristics:

i) Ancient Tista extend upto Bogra.

ii) In this area shallow depression are found.

iii) Almost entire area flooded during monsoon.

b) Old Brahmaputra Flood Plain [7, 9]

Area: From the south western corner of Garo Hulls along the eastern part of Madhupur tract.

Characteristics:

i) Composed of broad ridges and depression.

ii) In case of depression flood occur more than 1m.

iii) In ridges shallow flooding occur only in monsoon.

c) Jamuna Flood Plain [8]

Area: In 1787, Brahmaputra changes its course and shifted to the western side of Madhupur

to the eastern side, which is now called Jamuna.

Characteristics:

i) Major flood plain.

ii) Generally flooded during monsoon.

d) Ganges Flood plain [11, 12]

Area: From the western border of the country to the south of Barind tract.

Characteristics:

i) The series of high levels on its northern bank Between 25-30m above MSL.

ii) Gentle slope towards the north.

The annually flooded areas south of the Ganges already belong to moribund portion of the

delta.

e) Meghna Flood Plain [16, 17]

Areas: From the South-West to South-East of Dhaka, Meghna is the combination of Ganges

and Jamuna.

Characteristics:

i) Gentle slope towards South-East Direction.

ii) Annually Flood occur during monsoon.

3. Barind Tract [25, 26, 27]

Area: North of Rajshahi, Westerns part of Bogra, South-West part of Rangpur and the South

of Dinajpur.

Characteristics:

i) Area is around 10,000 sq. km

ii) Height is 45m above MSL

iii) Reddish and yellowish clay.

iv) Not subjected to annual flood.

4. Madhupur Tract [28]

Location: Area is 1585 sq. miles and situated to the North of Dhaka city.

Elevation: 20-100 ft

Madhupur High Land

Madhapur Garh Bhawal Garh Dhaka Terrace

(North of Dhaka City) (In the middle of Dhaka) (South of Dhaka)

Characteristics of Madhupur Garh:

i) High elevation.

ii) Area has been dissected by Bansi, Turag, Khiro and Banar rivers and their tributaries.

iii) Slope ranges from 280- 350

iv) It contains red clay

Characteristics of Bhawal Garh:

i) Consists of Joydevpur, Sreepur, Tongi, Savar and Kapasia areas.

ii) Elevation lower than Madhupur Garh.

iii) Low Gradient.

iv) Area is dissected by Turag river systems and tributaries of Sitalakya.

v) Contains moist red clay.

5. Foothills of Shillong Massif [22]

- Garo hills

-Khasi hills

-Jainia hills

Mostly in Indian parts

6. Haor Basin [20, 21]

Area: Sylhet, Moulovibazar, Hobigonj, Sunamgonj, Kishorgonj nad Netrokona.

Characteristics:

i) A large Gentle depressional featureis bounded by old Brahmaputra

ii) Numurour Bills and Haors Are located

iii) Height 3m above MSL

iv) Tila are situated in Sylhet

7. Tippera surface [22]

Area: The area between Meghna flood plain and Tripura hills is uplifted.

Majorly 2 parts

i) Tippera surface

- Made up of estuarine sediments of early recent time

- Foe irrigation purpose this land artificially created to a rectangular drainage pattern.

ii) Lalmai Terrace:

- Situated 8 km south from Comilla.

-Red clay

-Elevation is 6 to 50m above MSL.

8. Delta

i) Moribund delta

ii) Central deltaic basin

iii) Immature delta

iv) Mature delta

v) Active delta

In our country mature and active delta are frequent. They include following zones:

Mature delta:

a) Old Ganges flood plain [13]

b) Padma-Modhumoti flood plain [13]

c) Non-saline tidal flood plain [13]

d) Saline tidal flood

Active delta

a) Active Padma flood plain [10]

b) Meghna estuarine islandsand Shoals and bars

c) Meghna estuarine flood plain