Unit #10: Weathering, Erosion, Deposition and Landscapes

Why do rocks weather?    rocks below the

surface are protected from the exposure to wind, water and biological processes

once uplifted and exposed rocks begin to weather

Weathering

the breakdown of rock due to physical or chemical changes

Physical Weathering

changes the size and/or shape of a rock, without changing the rock’s chemical composition

Example: breaking a rock into smaller pieces

harder minerals are more resistant to physical weathering

Types of Physical Weathering:

Frost action alternating temperatures above and below 0C, allow water to melt and freeze, causing expansion of the cracks

Biological Factors roots of plants can grow within cracks in the rocks and increase the crack size, leading to crumbling of the rock

Abrasion collisions between particles caused by wind, moving ice and gravity, these particles act like sandpaper of the rocks

Chemical Weathering

changes in the chemical composition of rock, thereby forming new substances.

Example: rusting of iron rich mineral

    chemical weather requires heat and water    some minerals are more resistant to chemical weathering, such as quartz    slightly acid water can cause significant weathering of limestone forming caves    emissions of atmospheric pollutants such as oxides of sulfur and nitrogen can cause rain to be acid and increase chemical erosioncarbonic, nitric, and sulfuric acid are able to change hard limestone into a soft residue

Chemical Weathering

How do soils form?

Soil --> mixture of weathered rock and organic remains that usually cover bedrock

Develop through:

      physical weathering

      chemical weathering

      organic activity

Nature of soils dependent upon:

      rocks from which it weathered

     local climate

amount of organic activity (plants and animals)

Soils Horizons

--> distinct layers of soil created by different amounts of organic and inorganic material

Thickness of Soil horizons

      young/immature soils do not show distinct horizons      mature soils show distinct A, B, and C horizons      arid climates have thin soils      humid climates have thick soils      steep sloping areas have thin soils gentle sloping areas have thick soils

Escarpments in an arid climate

--> Soils must be conserved from wind and water erosion

--> it takes between 100 and 400 years for one centimeter of topsoil to form

--> Conservation methods include:

      Contour farming

      Terracing

      Increase vegetation cover

      Wind blocks

Types of Soils

Residual soils --> form directly above the parent bedrock, thinner

Transported soil --> form from sediments that has been moved into that area

How are weathered Material Transported?

Sediments --> rocks that have been broken into fragment, regardless of their size

Erosion

--> the transporting of sediments away from their place of origin and the depositing of them elsewhere

Force behind erosion: gravity

Example: rock falling from a cliff

Water moving down slope

Erosion by Water

Watering is the primary agent of erosion on the Earth’s surface

each year streams and rivers carry millions of tons of sediments downstream and into the oceans

Transportation of sediments by water:

1) Solution --> smallest particles dissolved in the water, can’t be filtered

2) Suspension --> large particles, not dissolved, can be filtered

3) bouncing and rolling --> largest particles will travel along the bottom of the stream channel

      Faster moving water carry larger particles and small particles

Slower moving water carry small particles, only

The Velocity of Streams.      controlled by the slope of the landscape and the volume of water

      Stream gradient increases, water velocity increases

Increase volume of water will also increase velocity

Discharge

--> volume of water that is traveling in a stream

Increases with velocity and volume

Speed of water

Equilibrium exists between the force of gravity and the friction created by the channel

In a straight stream, water will flow the fastest in the middle of the channel, less friction

Meandering Stream

--> curving stream path

Erosion on the outside of the turn, velocity is fastest

Deposition on the inside of the turn, velocity is slowest

•

--> Gentle valleys, like Milford, will have meandering stream, more horizontal erosion

--> Steep valleys, like ravine behind the school, has straighter streams, more vertical erosion

Erosion By Wind

--> pick up loose rock materials such as sand, silt and clay and carry them away

--> occurs in arid climates with little vegetation

--> erosion of clay and silt (smallest) particles leaving behind only larger particles called: desert pavement

--> can also erode by abrasion--> similar to sandpaper rubbing

against a rock creating angular, but smooth sediments called: ventifacts

Erosion by Ice

--> when the snow during the winter does not melt during the summer and begins to accumulate year after year--> Ice can get up to a mile thick--> Ice will start to move down slope under its own weight

--> Glaciers will trap all sizes of sediments within the ice, creating a massive piece of sandpaper that will scour the valley it travels through

Evidence of Glaciation--> Glaciers will deepen and widen preexisting valley to

give them a characteristic U-shape.--> Stream cut through valleys with vertical

erosion to create a V-shapeUnsorted deposits --> deposition of sediments of

all sizes in one areaStriations --> scratches in the bedrock caused by

the rough undersurface of the parallel grooves that align with the glaciers movement--> In NYS these striation run from NW to SE, indicating that the last glacial advancement came from Canada

Four Periods of continental glaciation in the past two million years in NYS

      due to glaciation, NYS is covered with thick transported soils

The last glacial advancement was the Wisconsin glacier approximately 11,500 years ago

o       Created U-shaped valleyso       Rounded mountain topso       Polished bedrock with striationso       Unsorted sedimentso       Long Island and Cape Codo       Finger lakeso       Thick transported soilsLarge miscellaneous boulders called: Glacial erratic

What is depositions?

Deposition --> when an agent of erosion deposits, or lays down, particles and fragments of earth materials

  also called sedimentation most deposition

occurs in water

Factors that affect deposition

Rate of deposition is dependent upon factors such as:

      Size

      Shape

      Density

Speed of the transporting material

Particle Size:

--> Inverse relationship

      large a particles settle first, while small particles settle last

particles in solution or suspension may stay suspended indefinitely

Particle Shape:

--> flat, angular and irregularly shaped particles settle more slowly than smooth, rounded particle

Particle Density

--> denser particles settle faster

--> less dense particles settle more slowly

Settling Rate and Settling Time

--> Inverse relationship

--> faster rate indicates less settling time

--> slower rate indicates more settling time

Settling Time of Particles

Mass (g) (Size)

Tim

e

Settling Rate of Particles

Mass (g)(Size)

Rat

e (m

eter

s/se

c.)

Sorting of Sediments

--> velocity of transporting material plays a major role in determining when deposition of particles will occur

--> initiated by a reduction in velocity

Stream is moving at a velocity of 500 cm/secit is carrying all sized particles.

Slow down, drop sediment load

Pebbles

Sand

Silt

Clay

Horizontal sorting sorting with largest, densest and roundest first and then farther out the smallest, least dense and flattest particles farther out (horizontal arrangement)

Vertical sorting (graded bedding)

particles are deposited in layers with the largest, densest and roundest particles on the bottom and then the smallest, least dense and flattest particles on top

Example: dropping a mix of particles into water (can be repetitive)

Deposition by streams:

Sandbars shallow area in a stream due to low water velocityo       frequently dredged to keep the stream deep

Delta deposits created when a stream enters a larger body of watero       land around the mouth of the Mississippi is a delta, New Orleans, Mississippi delta is thousands of square miles

Deposition by Wind

    generally sorted by size and located in arid climates

wind leaves behind larger sediments creating

Sand dunes

hills of wind blown deposits

Deposition by Gravity

    gravity pulls sediments toward the Earth’s center, they are not sorted when deposited by gravity, angular

Deposition by Glaciers

    deposition occurs when the glacier melts leaving behind eroded sediments

    unconsolidated and unsorted

Glacial erratic large rocks that have been transported by glacial ice

Adult person

Two types of Glacial sediments:

1) unsorted sediments deposited directly by the glacier

2) sorted sediments deposited by the moving melt water of the glacier

New York and The Ice Ages

    NYS’ climate has changed over the last 2 million years causing 4 different ice ages

    Accumulation of snow and ice creates a glacier that will then begin to move to lower elevations due to its own weight

    When the climate warms again, glaciers melt, releasing tremendous amounts of water causing even more erosion

Types of Glaciers:

1) Alpine glaciers (valley glaciers) occur in mountain regions

2) Continental glaciers (ice sheets) large glaciers that start in colder regions and move down slope this type of glacier produced most of NYS

glacial features

Evidence of Glaciation in NYS

U-shaped valleys

glacial polish, rounded hills: bedrock that has been smoothed by the scouring action of the ice and collected sediments

striations grooves and scratches in the bedrock, indicate the direction of flow

drumlins small rounded mounds created when a glacier goes over hills of unconsolidated sediments

Evidence of Glaciation in NYS

moraines unconsolidated, unsorted sediments that were pushed forward by the glacier as it advanced

o       form Long Island and Cape Cod

o       created the valley head moraine, which allowed for the formation of the Finger Lakes

outwash plan area of sorted sediments created by glacial melt water

Evidence of Glaciation in NYS

The Oceans and Costal Processes

    Earth is 71% covered by seawater

    Average depth 3 miles

    Most sediments from land will be eroded to the oceans

Edges of the oceans are places of rapid change caused by the action of waves and longshore currents.

Waves

water does not move forward with the waves, but circulate transferring energy

    movement of waves and longshore currents create many typical features along the shoreline

 

humans love to live near the ocean, but the rapid rate of erosion cause destruction of property

    humans build structures to reduce the damage created by waveso       breakwaters – shelter harbors, boats jetties – build to keep sand from eroding away from the beach

What is a Landscape?

Landscape a region on Earth’s surface in which physical features, such as hills, valleys and streams are related by a common origin

Topography general shape of the landscape

    landscape features are determined by:

o       climate

o       bedrock

o       geologic structures

o       human activities

Landscape regions:Mountains greatest relief, often

igneous and metamorphic or nonhorizontal sedimentary rocks Example: Rockies, Adirondacks, Alps, Himalayas

Landscape regions:Plateau relatively flat or rolling uplands, underlain by flat sedimentary bedrock

Example: Milford area, Grand Canyon

Landscape regions:

Plains little topographic relief, flat low elevation

Example: Florida & Midwest

The Influence of Climate    humid areas have more rounded landscapes

arid areas have more sharp angles and steeper slopes to the landscape

Moisture is important to the rate of chemical weathering

    causing more rounded landscapes

    thicker soils

promotes plant growth

Arid environments produce:

    greater amounts of physical weathering

    thin soils

    deserts have the most rapid stream erosion after a rainfall

Landscapes of the United States

abrupt changes in landscape is a result of change in the bedrock

How do geologic Factors influence the landscape?

    within the same climate landscape regions can develop very differently    hard minerals create rocks that are very resistant to weathering and erosiono       creating cliffs or escarpments near regions of less resistant rockstreams also follow areas of weaker, softer rock

Landscapes affect drainage patterns

Landscapes of New York StateSt. Lawrence/ Champlain Lowlands plains areas, predominantly layers of sedimentary rocks

Appalachian Uplands (Allegheny Plateau)

largest landscape region in NYSo       underlain by flat layers of sedimentary rockso       landscape have been uplifted 1000 of meters, which were later eroded by streams (dissected plateau)Finger lakes have been eroded out of this landscape

Erie-Ontario Lowlands

areas south of these lakes

o       created by sediments left by glacial meltwater

great soils for agricultural purposes

Adirondack Highlands

o       only true mountain landscape in NYSo       uplifted ancient metamorphic and igneous rocks creating a domeo       very hard and resistant to weatheringNYS highest mountain: Mount Marcy (5240 feet)

Landscape vs. Age

Streams will continue to erode an area to produce a wide flat valley and many meanders in the stream