Exogenic Processes: Mass Wasting Quiz

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Questions and Answers

What is mass wasting primarily driven by?

Human activity

Wind erosion

Gravity (correct)

Temperature variations

Which of the following factors reduces shear strength in saturated soil?

Increased vegetation

Higher soil density

Decreased temperature

Increased pore pressure (correct)

What happens when shear resistance is less than shear force?

Stable soil formation

Soil fertility increases

A landslide occurs (correct)

Erosion prevention

Which of the following is NOT a common trigger of mass wasting?

Volcanic eruptions Signup and view all the answers

How does gravity affect shear forces on steep slopes?

It maximizes shear force Signup and view all the answers

What role does a small amount of water play in soil movement?

It prevents downslope movement Signup and view all the answers

What is the most avoidable major geologic hazard mentioned?

Mass wasting Signup and view all the answers

Which of the following terms is associated with resistance to movement in mass wasting?

Shear strength Signup and view all the answers

What characterizes the movement of bedrock, rock debris, or soil in mass wasting?

Downhill movement caused by gravity Signup and view all the answers

Which condition can lead to an increase in shear force during mass wasting?

Increase in slope steepness Signup and view all the answers

What role does vegetation play in the stability of soil during mass wasting events?

Provides roots that hold soil together Signup and view all the answers

Which of the following is a direct trigger of mass wasting?

Seismic activity Signup and view all the answers

How does saturated soil affect its shear strength?

It reduces shear strength due to increased pore pressure Signup and view all the answers

What happens when shear resistance is equal to shear force in the context of mass wasting?

No movement occurs Signup and view all the answers

Which factor is considered the primary driving force behind mass wasting?

Gravity Signup and view all the answers

What effect does heavy rainfall have on mass wasting?

It increases the likelihood of landslides Signup and view all the answers

Study Notes

Exogenic Processes of the Earth: Mass Wasting

Mass wasting is the downhill movement of bedrock, rock debris, or soil caused by gravity.
It's a major geologic hazard.

Controlling Factors in Mass Wasting

Driving Force: Gravity
- Slope angle: Steep slopes increase instability.
- Local relief: High relief regions are more prone to mass wasting.
- Bedrock thickness: Thick layers of soil increase instability.
- Orientation of planes of weakness in bedrock: Planes parallel to the slope are more stable.
Contributing Factors
- Thickness of soil over bedrock
- Orientation of planes of weakness in bedrock
- Climatic factors (ice in the ground, water in soil, precipitation)
- Vegetation
Stable Situations
- Gentle slopes or horizontal surfaces
- Low thickness of soil
- Planes at right angles to the slope
Unstable Situations
- Steep or vertical slopes
- High thickness of soil
- Planes parallel to the slope

Shear Strength and Water

Shear strength is the resistance to movement or deformation.
Saturated soil has reduced shear strength due to increased pore pressure.
A small amount of water can prevent downslope movement (e.g., building a sandcastle).

Mass Wasting Triggers

Seismic activity
Heavy rainfall
Construction
Lack of vegetation

Classification of Mass Wasting

Rate of movement: from <1 cm/year to 100 km/hour.
Type of material: Solid bedrock or debris (unconsolidated material).

Types of Mass Wasting

Flow: Mass movement where material moves as a viscous fluid. (examples: earthflow, debris flow, mudflow)
Slide: Mass movement where material moves along a well-defined surface. (examples: translational slide, rotational slide)
Fall: Mass movement where material freely falls. (examples: rockfall, rockslide)

Preventing Landslides

Remove loose material
Stitch slopes together
Construct retaining walls with drains

Streams and Floods: Hydrologic Cycle

Movement and interchange of water between the sea, air, and land.
Includes Evaporation, Precipitation, Transpiration, Runoff, Infiltration.

Streams and Floods: Running Water

Stream: A confined body of running water, flowing under gravity.
Headwaters: Upper portion near the source, often in mountains.
Mouth: Where a stream enters a larger body of water(e.g., lake, ocean).
Channel: Narrow eroded depression.
Stream banks: Sides of a channel.
Streambed: Bottom of the channel.
Floodplain: Flat area created by sediments deposited during floods.

Drainage Basins

Total area drained by a stream and its tributaries (smaller streams that join the main one).
Divides (high ground) separate drainage basins.

Drainage Patterns

Dendritic: Branching pattern resembling a tree.
Radial: Streams diverge outward like spokes from a center point.
Rectangular: Streams often intersect at right angles.
Trellis: Parallel streams with tributaries meeting at right angles.

Factors Affecting Stream Erosion and Deposition

Velocity
Discharge
Gradient
Channel shape and roughness

Stream Transportation of Sediment

Bed load: Large, heavy particles moving along the streambed.
Suspended load: Smaller, lighter particles suspended in the flowing water
Dissolved load: Dissolved minerals carried in solution.

Stream Deposition

Bars: Temporary sediment deposits along the stream course.
Place deposits: Concentrated heavy sediment at a location.

Braided Streams

Interconnected rivulets (small streams) with numerous bars around which water flows.
Common in areas with high sediment loads.

Meandering Streams

Pronounced sinuous curves (meanders).
Erosion on the outside of bends creating cutbanks
Deposition on the inside creating point bars.

Meandering Cutoffs

When a new, shorter channel cuts across the neck of a meander, creating an oxbow lake.

Floodplains

Broad areas of land built up by sediments deposited on either side of a stream channel
Form during floods when water overflows from its channel
Natural levees slightly raised areas along the main channel

Deltas

Deposits of sediment at the mouth of a river when the flow velocity decreases.
Shape depends on whether wave, tide or stream-dominated.

Alluvial Fans

Fan-shaped sediment deposit where a stream flows from a steep slope onto a flatter surface.

Stream Valley Development

Downcutting: Deepening of the valley by stream erosion
Headward erosion: Uphill extension of a valley.
Grading: A balanced state where sediment load matches transporting ability.
Terraces: Step-like landforms above a stream and its floodplain

Floods

Occurs when water levels rise and overflow stream banks due to increased volume or discharge.
Natural process but can cause significant damage in populated areas.

Flooding and Urbanization

Urbanization increases runoff and speeds up waterflow to streams thus increasing flash flood potential.

Flash Flooding

Sudden, high-volume, short-duration flood often caused by heavy thunderstorms.

Reducing Flood Risk

Dams to store water and regulate release.
Artificial levees but need management to avoid downstream risk.
Wise land-use planning, including avoidance of development near floodplains.

Impact of Dams

Social benefits (electricity, water supply).
Environmental concerns (sediment trapping, habitat loss).

the Importance of Groundwater

Lies beneath the surface, filling pores in sediments and rocks.
Important resource for drinking water, agriculture, and industry.
Supplies approximately 1.7% of the hydrosphere.

Contaminants in Groundwater

Infiltrating water carries pollutants like pesticides, fertilizers, heavy metals, and industrial chemicals.

Balancing Withdrawal and Recharge

Crucial to sustain groundwater resources for future use. Should never be withdrawn faster than replenished.

Geologic Effects of Groundwater

Dissolves soluble rocks (e.g., limestone, creating caves, sinkholes)
Subsidence: Ground sinking due to the removal of groundwater
Changes in the base level
Creates karst formations

Porosity and Permeability

Porosity: Percentage of void space in a rock.
Permeability: Rock's ability to transmit fluid through its pores.

Aquifers and Aquitards

Aquifer: Permeable rock layer containing groundwater used for wells.
Aquitard: Impermeable rock layer that restricts groundwater flow.

Movement of Groundwater

Groundwater moves through pores and fractures at a relatively slow rate (cm to meters per day).
Rates increase in highly permeable materials like caves and fissures.

Wells

Deep holes dug or drilled to access groundwater in aquifers to obtain water.
Water level in an unconfined aquifer is at the water table.
Pumping can lower the water table (drawdown).

Glaciers and Glaciation

Large, long-lasting masses of ice that move under their own weight.
Types: Alpine (mountain valleys) and Continental (large, ice sheets).

Distribution of Glaciers

Most extensive in polar regions but can occur wherever snow accumulation exceeds loss throughout the year.

Formation and Growth of Glaciers

Snowfall is compacted and recrystallized into granules and then firn before forming glacial ice.
Gravity moves glaciers downslope.

Glacial Budget

Advances or retreats based on relative accumulation and ablation or ice loss.

Movement of Valley Glaciers

Move downslope due to gravity, including Basal sliding and plastic flow patterns.

Movement of Ice Sheets

Move downslope and outward from a central high area due to both basal sliding and plastic flow.

Glacial Erosion

Glaciers erode rocks and other material as they move, including Plucking and Abrasion, forming U-shaped valleys and polishing rocks

Glacial Deposits

Glacial till: Unsorted and unlayered sediment deposited by the glacier. Includes Moraines that form at the sides of or at the terminus of the glacier.
Outwash: Sediment transported and deposited by meltwater from a glacier, usually found as braided stream deposits.
Varves: Alternating layers of coarse and fine sediment in glacial lakes.

Glacial Valleys

U shaped valleys formed by deep glacial erosion.
Associated with alpine glaciation.
Features include hanging valleys, truncated spurs, cirques, horns and arêtes

Landscapes Associated With Continental Glaciation

Rounded topography, grooved or striated rock surfaces are common features formed by moving glaciers.

Glacial Deposition: Outwash

Sediment deposited by glacial meltwater.
Forms braided stream patterns and features like eskers, kettles, and kames

Past Glaciation

Extensive ice ages in the Earth's past. Evidenced by tillites, moraines and glacial-carved landscapes
Hypothesized by scientists like Louis Agassiz.

Deserts and Wind Action

Deserts: Receive less than 25 cm of precipitation per year and are primarily shaped by wind and infrequent water erosion
Wind: Principal erosional and depositional agent. Transports sediment, leading to features like blowouts, desert pavement, or loess.
Types of Desert Landscapes: Based on rainfall and climate characteristics.

Wind Erosion and Transportation

Wind can keep dust in suspension at low speeds, but higher winds cause saltation or sand grains move by bouncing or skipping along.
Sandblasting rocks by suspended grains, creating ventifacts.
Deflation: Removal of fine sediments
Desert paving: Remaining coarse material after fine sediments have eroded.

Wind Deposition: Loess

Unweathered grains of quartz, feldspar, etc.
Often fertile due to mineral content but is easily eroded.

Wind Deposition: Sand Dunes

Mounds of loose sand, shaped and moved by wind.
Types: Barchan (crescent), Transverse(straight), Parabolic (U-shaped)
Crosswinds shape them.

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Description

Test your knowledge on mass wasting, a significant geologic hazard caused by gravity. This quiz covers the driving and contributing factors of mass wasting, along with stable and unstable situations. Understand how these processes affect our environment.