Surface Processes

Mass Wasting Streams Ground Water (Glaciers) (Shorelines) (Deserts)

Monument Valley, Arizona

Stream Carved Landscapes

Three Sisters, Cascades, Oregon

Denali National Park, by Berann

Yosemite, Bridal Vail Falls

Karst Topography from GW action

XI. Mass Wasting

A. Classifications (Definitions, processes and controlling factors)

B. Examples (Appling knowledge of processes)

C. Prevention of Mass Wasting (limiting and eliminating)

Flow

Fall

Classification of Mass Wasting

Slide

Classification of Mass WastingT

ype

of

Mo

vem

ent

Classification  Material  Velocity  Creep Debris Imperceptibly Slow

Earth Flow Debris Slope and Material Dependent <5 km/hrMudflow Saturated Debris

Avalanche Debris or Rock Very Fast 100 km/hr

  Rotational Slide Debris Slow-mod. (short)

Rock Slide Bedrock Fast

  Debris Fall Debris Fast

Flo

wS

lide

Fal

l

Rockfall Bedrock Fast

Creep Imperceptibly slow flow Expansion - contraction

Heating – Cooling Freeze – Thaw

Earth Flow andRotational Slide Debris (soil) both

slides and flows

Sliding Rotation

(tilting) Scarp

Flow Mixing Hum-

mocks

Rock Slide and Fall

Bedrock may slide and/or fall

Weathering reduces bedrock strength

Eventually gravity wins

Talus Slopes

The result of Mechanical

weathering Rock falls and slides Crushing and

abrasion (more mechanical weathering)

Rock Avalanches Slopes of rock

fragments may let go and careen downhill as a very fast flow

Mass Wasting, Who Cares?

Geology in the news? How does it effect you?

(Environmental Geology) Know where to look Understand risks Reduce and prevent risks Improve engineering

We need to understand how mass wasting works

Shear Force vs. Shear Strength

Driving Forces i.e., Shear Force Component of Gravity Other forces

Resisting Forces i.e., Shear Strength Fiction and Adhesion Soil or Rock

Mt. St. Helens

Landslide triggers eruption Reduced shear

strength from earthquakes and bulging

Increased shear force as bulge grows and slopes steepen

Eruption causes Mudflows

Gros Vantre Slide

Sandstone and debris on Impermeable shale

Saturation of sandstone and lubrication of shale

Both reduced shear strength (added to shear force)

Shear force overcomes shear strength

Sandstone and debris slide

Use Knowledge of Mass Wasting to Avoid Risks

Be able to recognize geologically unstable situations

Understanding Mass Wasting

Development causes: Increased shear force

Steepened slope Added weight

Decreased shear strength Devegetation Reworking of fill Saturation of soil

Reduce Risks

Some solutions include: Increase shear strength

Re-compact soils Re-vegetate soil slopes Construct retaining wall with

anchors Prevent Saturation

Prohibit over-irrigation Install surface drains Install subsurface drains

Increase shear strength with iron rods and anchors

Remove risk

Reduce Risks

Examples of Mass Wasting

The Old Man of the Mountain, Cannon Mtn. NH

X. Streams

A. The Hydrologic Cycle (components and pathways)

B. Stream Velocity (controls and results)

C. Drainage Patterns and Landscape Features (results of erosion and deposition)

D. Stream Valley Development (tectonic uplift and downcutting)

The Hydrologic Cycle See Fig. 12.3

Systems of streams and their tributaries that collect runoff Divide Ground Water

Drainage Basins

Great LakesDrainage Basin

Steam Profiles(Streams Shaping

the Land)

V-Shaped Valley

FloodPlain

What is this Drainage Pattern?(What does is tell of the geology?)

Valley and Ridge Province of PA(Trellis Stream Patters)

Stream Gradient

Slope of the land Sinuosity of stream

10 m/km 10 m per 1¼ km =

8 m/km

10 m

1 km

10 m

1 km

Meander Velocity

Higher velocities on outside of meanders causes erosion (cut bank)

Lower velocities on inside of meanders causes deposition (point bar)

Fig. 10.6

Channel Shape and Roughness

A. Narrow and Deep Less resistance Faster flow

B. Wide and Shallow More resistance Slower flow

C. Rough Streambed More resistance Slower flow

Stream Velocity Controls:

Erosion Transport Deposition

Stream Erosion

Then, Erosion Solution (chemical weathering) Hydraulic Action (lifting) Abrasion (crushing and grinding)

Fig 10.11

First, Weathering Fracturing

(mechanical) Loosening

(mechanical and chemical)

Solution (chemical)

Stream Transport

Dissolved Load Suspended Load Bed Load

Saltation Rolling, sliding

Fig10.14

(ions)

Stream Deposition

BraidedStreams

Alluvial Fan

e.g., Alluvial Fans

Fig. 10.31

Fig. 10.19

Erosion Dominated High gradients Less resistance Fast velocities

Deposition Dominated Lower gradients More resistance Lower velocities

Stream Deposition

Midchannel bars Fig. 10.18a

Point bars

Fig 10.22b

Braided streamsFig. 10.18b

Deltas

Fig. 10.28

Reduction of velocity due to extreme widening

Deposition of silt and clay

Erosion and Deposition Transport

E.g., Meandering streams As meanders are

migrating Cutbanks eroding Point bars building

Sediment is moving downstream

Meander Cutoff

How does the gradient change with meandering and meander cutoff?

Meandering Streams

Identify Cutbanks Point bars Meander neck Oxbow lakes Areas of Erosion Areas of

Deposition

Fig. 10.20

AA

BBCC

DD

EE

Flooding Overbank deposits Widening of stream

into flood plain Deposition of

sediment Coarse near stream Fine farther away

Natural Levees

Fig. 10.27Fig. 10.27

Graded Streams

Increased velocity and accelerated erosion.

Erosion acts to grade the Longitudinal stream profile to concave-upward curve

Base level:Lake or Sea

Same Base level

Drainage PatternsGeology controls stream patternsA. Uniformly Erodible

(e.g., flat-lying sedimentary rocks of the Midwest)

B. Conical Mountains (e.g., Volcanoes)

C. Fractured bedrock(shallow bedrock)

D. Resistant ridges of tilted sedimentary rocks(e.g., Valley and Ridge Province of Pennsylvania)

A. Dendritic

B. Radial

C. Rectangular

D. Trellis