surface processes mass wasting streams ground water (glaciers) (shorelines) (deserts)
TRANSCRIPT
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Surface Processes
Mass Wasting Streams Ground Water (Glaciers) (Shorelines) (Deserts)
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Monument Valley, Arizona
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Stream Carved Landscapes
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Three Sisters, Cascades, Oregon
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Denali National Park, by Berann
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Yosemite, Bridal Vail Falls
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Karst Topography from GW action
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XI. Mass Wasting
A. Classifications (Definitions, processes and controlling factors)
B. Examples (Appling knowledge of processes)
C. Prevention of Mass Wasting (limiting and eliminating)
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Flow
Fall
Classification of Mass Wasting
Slide
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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
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Creep Imperceptibly slow flow Expansion - contraction
Heating – Cooling Freeze – Thaw
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Earth Flow andRotational Slide Debris (soil) both
slides and flows
Sliding Rotation
(tilting) Scarp
Flow Mixing Hum-
mocks
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Rock Slide and Fall
Bedrock may slide and/or fall
Weathering reduces bedrock strength
Eventually gravity wins
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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
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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
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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
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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
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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
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Use Knowledge of Mass Wasting to Avoid Risks
Be able to recognize geologically unstable situations
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Understanding Mass Wasting
Development causes: Increased shear force
Steepened slope Added weight
Decreased shear strength Devegetation Reworking of fill Saturation of soil
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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
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Increase shear strength with iron rods and anchors
Remove risk
Reduce Risks
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Examples of Mass Wasting
The Old Man of the Mountain, Cannon Mtn. NH
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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)
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The Hydrologic Cycle See Fig. 12.3
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Systems of streams and their tributaries that collect runoff Divide Ground Water
Drainage Basins
Great LakesDrainage Basin
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Steam Profiles(Streams Shaping
the Land)
V-Shaped Valley
FloodPlain
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What is this Drainage Pattern?(What does is tell of the geology?)
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Valley and Ridge Province of PA(Trellis Stream Patters)
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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
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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
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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
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Stream Velocity Controls:
Erosion Transport Deposition
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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)
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Stream Transport
Dissolved Load Suspended Load Bed Load
Saltation Rolling, sliding
Fig10.14
(ions)
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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
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Stream Deposition
Midchannel bars Fig. 10.18a
Point bars
Fig 10.22b
Braided streamsFig. 10.18b
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Deltas
Fig. 10.28
Reduction of velocity due to extreme widening
Deposition of silt and clay
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Erosion and Deposition Transport
E.g., Meandering streams As meanders are
migrating Cutbanks eroding Point bars building
Sediment is moving downstream
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Meander Cutoff
How does the gradient change with meandering and meander cutoff?
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Meandering Streams
Identify Cutbanks Point bars Meander neck Oxbow lakes Areas of Erosion Areas of
Deposition
Fig. 10.20
AA
BBCC
DD
EE
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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
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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
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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