Mass Wasting and Flood Management Quiz

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Questions and Answers

What is the primary driving force behind mass wasting?

Gravity (correct)

Shear strength

Weight of material

Friction

Which of the following factors can trigger mass wasting?

Regular maintenance

Earthquakes (correct)

Wind erosion

Lack of sunlight

How does saturation of soil affect its shear strength?

Has no effect

Decreases shear strength (correct)

Makes shear strength variable

Increases shear strength

What characterizes soil creep in mass wasting?

Very slow downslope movement Signup and view all the answers

What type of mass wasting occurs when debris moves downslope as a viscous fluid?

Flow Signup and view all the answers

Which of the following contributes to decreased resistance to downhill movement in saturated soil?

Increased pore pressure Signup and view all the answers

What is a significant impact of creep on property structures?

Foundation cracks over time Signup and view all the answers

Which of the following types of mass wasting is common in colder climates due to the melting of permafrost?

Solifluction Signup and view all the answers

What primarily causes the formation of incised meanders?

Rapid tectonic uplift Signup and view all the answers

Which of the following is a natural process that can lead to flooding?

Water level rise that overtops river banks Signup and view all the answers

What is a significant effect of urbanization on flooding?

Increased impermeable surfaces Signup and view all the answers

Which flood management method is most effective in reducing flood risk?

Wise land-use planning Signup and view all the answers

What is a key environmental concern associated with dam construction?

Habitat destruction Signup and view all the answers

Why is groundwater considered a tremendously important resource?

It is generally cleaner than surface water Signup and view all the answers

Which of the following is NOT a societal benefit of dams?

Trapping sediment and nutrients Signup and view all the answers

What can trigger flash flooding?

Heavy thunderstorms Signup and view all the answers

What signifies an advancing glacier?

It gains more snow than it loses. Signup and view all the answers

Which process is responsible for the movement of glaciers downslope?

Gravity-induced movement Signup and view all the answers

What is the primary mechanism of glacial erosion?

Plucking and abrasion Signup and view all the answers

What best describes the equilibrium line in a glacier?

The boundary separating areas of accumulation and ablation. Signup and view all the answers

What characterizes a U-shaped valley formed by glaciers?

Flat bottom and steeply sloping sides. Signup and view all the answers

What is rock flour in the context of glacial erosion?

Fine rock powder produced during glacial abrasion. Signup and view all the answers

What distinguishes an outlet glacier from other types of glaciers?

It is a mountain valley glacier from higher elevations. Signup and view all the answers

In glacial movement, what does basal sliding refer to?

Sliding of the glacier over the underlying bedrock. Signup and view all the answers

What primarily determines the shape of a delta?

The type of dominant forces acting upon it Signup and view all the answers

Which of the following describes the primary process that forms V-shaped valleys?

Downcutting Signup and view all the answers

How does an alluvial fan develop?

When a stream emerges from a narrow canyon onto a flat plain Signup and view all the answers

What are stream terraces?

Step-like landforms above a stream and its floodplain Signup and view all the answers

Which of the following factors does NOT influence stream grading?

Stream width Signup and view all the answers

Which process is indicative of a stream that has reached base level?

Increased sediment deposition Signup and view all the answers

What is the primary cause of terrace formation in streams?

Rapid erosion into the floodplain Signup and view all the answers

What characterizes graded streams?

Concave-up longitudinal profile Signup and view all the answers

What is the most recent glacial age known to have peaked approximately 18,000 years ago known for?

Resulting in large-scale glaciation Signup and view all the answers

What are recessional moraines primarily associated with?

Retreating ice sheets Signup and view all the answers

Which of the following lakes is considered a glacial lake?

Lake Agassiz Signup and view all the answers

What geological effect is associated with the rebounding of the crust in the Great Lakes region?

Crustal rebound Signup and view all the answers

How many centimeters of precipitation defines a desert?

Less than 25 cm Signup and view all the answers

Which of the following regions is most commonly associated with desert formation?

Near 30° north or south latitude Signup and view all the answers

What type of sediment is represented by tillites?

Lithified glacial till Signup and view all the answers

What historical glaciation theory suggests that the oceans were once frozen over?

Snowball Earth hypothesis Signup and view all the answers

What primarily causes rain shadow deserts to form?

Moist air rising over high mountain ranges Signup and view all the answers

Which feature is typically associated with desert landscapes?

Intermittent stream flow Signup and view all the answers

What is a primary characteristic of the Colorado Plateau?

Features heavily eroded sedimentary rocks Signup and view all the answers

How does wind affect sediment in desert environments?

Keeps fine dust in suspension but moves sand grains by saltation Signup and view all the answers

What are alluvial fans formed from in desert regions?

Sediment deposited during heavy rain runoff Signup and view all the answers

What happens to sediment in playas within deserts?

Water evaporates, leaving behind minerals Signup and view all the answers

Which natural phenomenon is characterized by strong winds lifting fine sediments in arid regions?

Dust storms Signup and view all the answers

What is the primary composition of loess deposits?

Silt and clay composed of unweathered grains Signup and view all the answers

Study Notes

Exogenic Processes of the Earth

This course outcome covers the processes of mass wasting, streams and floods, and glaciers and glaciation.

Mass Wasting

Mass wasting is the downhill movement of rock, debris, or soil driven by gravity.
Proper planning can mitigate the risk of mass wasting.
Factors influencing the stability of slopes:
- Slope angle (steeper slopes are more unstable)
- Local relief (differences in elevation)
- Thickness of soil over bedrock (thicker layers are more susceptible)
- Planes of weakness in bedrock (faults, fractures)
- Ice in ground (freezing/thawing cycles)
- Water in soil or debris (saturation)
- Precipitation (heavy rainfall)
- Vegetation (vegetation helps stabilize slopes)

Controlling Factors in Mass Wasting

Most Stable Situation: Gentle slopes, horizontal surfaces, low thickness, and planes perpendicular to hillside slopes. Temperatures above freezing, light rainfall, and high vegetation.
Most Unstable Situation: Steep or vertical slopes, high thickness, planes parallel to hillside slopes, freezing/thawing, saturated soil, episodes of heavy precipitation, and sparsely vegetated slopes.
Triggers: Earthquakes, weight added to the slope, and heavy rainfall

Gravity, Shear Strength and Water

Gravity is the driving force behind mass wasting.
Normal force, shear force, and shear resistance are key components.
Shear resistance less than shear force indicates landslide potential.
Steep slopes exacerbate shear forces due to gravity.
Water saturation reduces shear strength, increasing the risk of slope failures.

Mass Wasting Triggers

Earthquakes
Heavy rainfall
Construction (adding weight)
Lack of vegetation (reduced stability)

Classification of Mass Wasting

Rate of movement: <1 cm/year to >100 km/hour
- Type of material: solid bedrock or unconsolidated material.
- Type of movement: flow, slide, or fall

Some Types of Mass Wasting

Flow: Creep (soil), Debris Flow, Earthflow, Mudflow, Rock Avalanche.
Slide: Debris slide, Rockslide.
Fall: Rockfall.

Creep (Soil Creep)

A very slow downslope movement of soil.
Caused by daily freeze-thaw cycles and water in soil.
Can damage structures over time.

Flows: Earthflow and Solifluction

Earthflow - debris moving downslope as a viscous fluid, can be slow or rapid.
Solifluction -flow of water-saturated soil over impermeable material. Common in colder, permafrost climates.

Flows: Debris Flow, Mudflow, Avalanche

Debris flow – mixture of debris and water, usually down a channel.
Mudflow – only soil and water mixture.
Debris avalanches – rapid, turbulent movement of debris.

Falls

Material free-falls or bounces down a cliff.
Rockfall – a block of bedrock that breaks free and falls.

Slides

Descending mass remains relatively intact, moving along well-defined surfaces.
Types include:
- Translational slide - movement along a plane parallel to the motion.
- Rotational slide (slump) - movement along a curved surface.
Also includes Rockslides, Rock Avalanches, and Underwater Landslides (turbidity currents, tsunamis).

Preventing Landslides

Prevent rockfalls, rockslides on highways by removing loose material and anchoring slopes.
Prevent mass wasting of soil by constructing retaining walls, avoiding oversteep slopes, and removing or stabilizing unstable rocks.

Streams and Floods

Stream- a body of running water that flows downhill.
Headwaters - the source of the stream, usually in mountains.
Mouth - where the stream ends, usually at a sea, lake, or a larger stream.
Channel - the long, narrow depression eroded by the stream.
Stream banks - sides of the channel.
Streambed - bottom of the channel.
Floodplain - flat valley floor composed of sediment deposited by the stream.

Hydrologic Cycle

The interconnected movement of water between the sea, air, and land.
Includes:
- Evaporation: Liquid water changes to water vapor.
- Precipitation: Water vapor falls to the Earth's surface as rain, snow, sleet, or hail.
- Transpiration: Water evaporates from plants, part of the water cycle.
- Runoff: Water traveling over the Earth's surface.
- Infiltration: Water soaking into the ground.

Drainage Basins

Drainage basin – the total area drained by a stream and its tributaries.
Tributary – smaller stream flowing into a larger stream.
Divide – ridge or high ground that separates one drainage basin from another.
Continental Divide – a major ridge that separates streams flowing into different oceans or seas.

Drainage Patterns

Dendritic – resembles branching tree pattern.
Radial – resembles spokes of a wheel from a central point.
Rectangular – frequent 90° bends, joining other streams at right angles.
Trellis – parallel streams with shorter tributaries joining at right angles.

Factors Affecting Stream Velocity and Deposition

Velocity: Maximum velocity is at the channel's center. Higher velocities erode and transport larger sediments, while lower velocities deposit finer materials.
Gradient: The slope of the land affects the velocity of a stream.
Channel Shape: The channel's shape and roughness affect the velocity and erosion capacity of the stream.
Discharge: The volume of water flowing past a specific point in a stream per unit time.

Stream Erosion

Streams cut their own valleys by:
- Hydraulic action (picking up and moving sediment)
- Solution (dissolving of rocks)
- Abrasion (grinding of channel by sediment load).
Potholes are eroded into streambeds by abrasive action.

Stream Transportation of Sediment

Bed load - large particles rolling, sliding, or dragging along the streambed.
Suspended load - small/light particles suspended in the water column by turbulent flow
Dissolved Load – dissolved ions in chemical weathering solutions.
Saltation load- medium sized particles bouncing along the stream bed.

Stream Deposition

Deposition of sediments happens along stream courses.
Bars – temporary sediment deposits.
Placer Deposits – concentrated heavy sediment.

Braided Streams

Highly interconnected, interwoven streams.
Often associated with streams carrying a large amount of sediment.

Meandering Streams

Meanders are pronounced bends in a river.
Water flows faster on the outside of meanders, causing erosion (cut-banks).
Water flows slower on the inside, causing deposition (point bars).
Meanders can migrate and become cut-offs leading to oxbow lakes during flood events.

Meander Cutoffs

Formation of a new shorter stream channel across the neck during a flood.
This results in a meander cutoff which is left behind as an oxbow lake.

Floodplains

Flat areas on either side of a stream channel, built up from flood deposition.
Natural levees - raised banks on the stream that retain floodwaters.
Sediments left during floods

Deltas

Formed from sediment deposited by a river as the flow velocity decreases at the mouth of a river into standing water (sea or large lake).
Shapes depend on if they are primarily driven by waves, tides, or stream flow.

Alluvial Fans

Large, fan-shaped or cone-shaped sediment deposits.
Form where stream velocity decreases as it leaves a mountain canyon.
Shows a grading pattern moving from coarser sediments closest to the mountain to finer ones further down valley.

Stream Valley Development: Downcutting

Downcutting is the process where a stream deepens its valley by eroding the streambed.
V-shaped valleys often result from downcutting combined with mass wasting and sheet erosion.
Stream valleys can’t be eroded deeper than the base level.

Stream Valley Development: Grading, Later Erosion, Headward Erosion

Graded streams - streams have a concave upward longitudinal profile.
Lateral erosion – widening stream valleys by undercutting streambanks and walls.
Headward erosion – the slow uphill growth of a valley.
Valley development depends on the erosional processes.

Stream Valley Development: Terraces

Terraces are step-like landforms above a stream and its floodplain,
Formed by a river rapidly cutting into its floodplain.
Can be caused by rapid uplift, drops in base level, or climate changes, leading to sudden changes from depositional periods to erosional periods

Stream Valley Development: Incised Meanders

Retain their sinuous pattern as they cut downwards.
May be from tectonic uplift which creates a significant difference between surface level and base level and causes downcutting.

Flooding

Water levels rising and overflowing stream banks.
A common and natural process on all rivers.
Great damage for heavily populated regions.
High velocity and large amounts of water erode the surrounding areas.
Slowing down of water during the flood event leads to deposition on floodplains.
Recurrence intervals can be used to describe the frequency of flood events.

Flooding and Urbanization

Urbanization increases peak discharge due to impermeable surfaces causing more runoff and faster water delivery.

Flash Flooding

Sudden, localized floods of high volume caused by heavy thunderstorms.

Reducing Flood Risk

Implementing strategies to lessen flood impact such as dams, artificial levees, and careful land-use planning.
Wise land-use planning is most effective, including preventing building in 100-year floodplains.

Impact of Dams

Societal benefits: generating electricity, regulating floods.
Environmental concerns: trapping sediment and nutrients, habitat destruction, potentially causing landslides and groundwater issues.

Groundwater

Water filling pores and fractures below the ground surface.
Groundwater accounts for 1.7% of the Earth's hydrosphere.
Replenished by precipitation infiltrating into the ground, and is generally cleaner than surface water.

The Importance of Ground Water

1.7% of the hydrosphere.
Resupplied by precipitation.
Generally cleaner than surface water
Accessed by wells
Essential resource; its use is increasing dramatically due to a growing population.
Pollution levels are increasing.

The Water Table

Top edge of the saturated zone.
Water level in lakes and rivers usually corresponds to local water table levels.
Unsaturated zone – region above.
Perched water table – a water-table separated from main water table by an unsaturated zone, caused by a lens of impermeable rock.

Springs and Streams

Springs – where water flows naturally from the ground.
Gaining streams – receive water from the saturated zone.
Losing streams – lose water to the saturated zone (e.g., through high infiltration during stream courses above the water table).
Stream beds can lie above the water table.

Contamination of Groundwater

Infiltrating water carries contaminants to the water table, containing:
- Pesticides, fertilizers
- Landfill pollutants, heavy metals
- Bacteria, viruses and parasites
- Industrial chemicals (PCBs, TC E)
- Acid mine drainage
- Radioactive waste, oil and gasoline

Pollution Caused by Pumping Wells

Pumping wells can lower the water table, increasing the risk for contamination through:
- City landfills
- Sewage
Saltwater intrusion.

Balancing Withdrawal & Recharge

Overdrawing groundwater resources faster than they are replenished.
Subsidence issues (cracking foundations, roads, pipelines).
Extreme groundwater pumping use for crop irrigation in dry regions.

Geologic Effects of Groundwater

Groundwater dissolves soluble rock (e.g., limestone), creating cave systems, sinkholes, and karst topography.

Caves

Naturally formed underground chambers.
Acidic groundwater dissolves limestone along joints and bedding planes.
Formations include: stalagmites (on cave floors) and stalactites (hang from ceilings.)

Cave Formation

Describes the process of how acidic groundwater erodes limestone.
Explains how water tables and cave formation coincide geologically.

Karst Topography

Areas with rolling hills, disappearing streams, and sinkholes, created by groundwater dissolving limestone.

Sinkholes and Karst Topography

Sinkholes – surface caves collapse
Karst topography – landscape associated with caves.

Other Effects of Groundwater

Preservation of Fossils
Petrified Wood
Concretions
Geodes

Hot Water Underground

Hot springs - springs where water temperature exceeds human body temperature. Typically sourced from heated groundwater circulation to deep crustal areas containing magma.
Geysers - hot springs intermittently erupting hot water and steam due to pressure buildup in the restricted groundwater pathways.
Minerals will often precipitate around the hot springs as water cools rapidly.

Geothermal Energy

Energy produced from using natural steam or superheated water.
No CO2 or acid rain is produced during its use.
Some toxic gases are produced in trace amounts but it is still considered a cleaner option compared to fossil fuels or other energy sources.
Superheated water can cause corrosion to equipment and pipes.

Glaciers & Glaciation

A large, long-lasting mass of ice formed on land that moves under its own weight.
Includes alpine glaciers in mountainous regions and continental glaciers covering large landmasses.
Approximately 70% of the Earth's fresh water is locked in glacial ice.

What is a Glacier?

Large, long-lasting masses of ice formed on land and that move downhill under their own weight.
Includes alpine glaciers in mountainous regions and continental glaciers in polar regions.

Types of Glaciers

Snow recrystallizes into firn and then glacial ice.
Alpine glaciation occurs in mountainous regions as valley glaciers.
Continental glaciation covers large portions of Earth's landmasses in polar regions.

Distribution of Glaciers

Most widespread in polar climates; can occur anywhere snow accumulated at a higher rate than what melts.
Approximately 10% of the Earth's surface is covered by glaciers.
Approximately 85% of global glacial ice located in Antarctica.
Melted glacial ice would raise global sea levels by ~ 65 meters.

Formation and Growth of Glaciers

Snowfall compacts, removing air, creates granular snow that eventually becomes firn and glacial ice.
Gravity causes downslope movement of glaciers.
Ablation through melting, evaporation, or ice calving are all forms of glacier loss.

Glacial Budgets

Advancing glacier (gains more snow than it loses): Positive budget.
Receding glacier (loses more water than it gains): Negative budget.
Zone of accumulation (snow added).
Zone of ablation (melting, ice calving, icebergs).
Equilibrium line (boundary between gain and loss).

Movement of Valley Glaciers

Move downhill due to gravity.
Basal sliding (sliding over underlying rock).
Plastic flow (movement within the ice).
Rigid zone (upper part of the glacier).
Crevasses – fractures in the upper rigid zone from glacier flow.

Movement of Ice Sheets

Move downslope and outward from a central high area due to gravity
Basal sliding, plastic flow and rigid zone are characteristic types of movement.
Differences in flow rates compared to alpine glaciers are significant and related to the different mechanisms of ice movement.
Ice streams occur at higher points in the ice sheet and flow faster compared to the surrounding ice.

Glacial Erosion

Glaciers erode by plucking (removing chunks of rock) and abrasion (grinding).
Basal abrasion smooths and striates bedrock and produces rock flour.

Glacial Valleys

Associated with alpine glaciers.
Several types of valley formations.
U-Shaped valleys, hanging valleys, truncated spurs

Cirques, Horns, and Arêtes

Cirques: Steep-sided, half-bowl-shaped recesses carved into mountains by glacial erosion.
Horns: Sharp peaks left after several cirques have cut back into the side of a mountain.
Arêtes: Sharp ridges separating glacial valleys.

Landscapes Associated with Continental Glaciation

Continental ice sheets leave a rounded and smoothed surface on the land.
Effects include grooved or striated rocks, rounded knobs.

Glacial Deposition: Moraines

Till: Unsorted glacial sediment deposited by ice.
Types of moraines: Lateral, medial, end moraines, and recessional moraines. Also characterized by ground moraines.

Glacial Deposition: Outwash

Outwash sediment deposited by meltwater.
Deposition by braided channels, common at the front of glaciers.

Outwash Landforms

Eskers(sinuous ridge), Kettles (glacial depressions), Kames (low glacial mounds).

Glacial Deposition: Lakes and Varves

Glacial lakes form from glacial processes.
Varves are annual sediment deposits or layers accumulating in glacial lakes; layered patterns that can be used for dating.

Past Glaciation

Extensive glaciation in the past due to changes in Earth's climate (e.g. the most recent ice age 18,000 years ago).
Evidence from the past supports the theory of glacial ages.
Support from locations such as Swiss Alps, Europe, and North America.

Direct Effects of Past Glaciation

Large scale glaciation affected the surfaces of continents such as North America.
Scraped off sediment and soil, leaving rock.
Gouged out lake basins in certain areas.

Indirect Effects of Past Glaciation

Glaciation and climate change contributed to formation of various glacial lakes such as Lake Agassiz, Missoula, Bonneville, and others.
Pluvial lakes existed in certain areas which are now dry (e.g. Utah, Nevada), resulting from changes in precipitation patterns.

More Indirect Effects

Fiords – drowned glacially carved valleys, produced by rising sea level.
Crustal rebound – the land continues to rise after ice sheets are removed (e.g. Great Lakes region).

Evidence for Older Glaciation

Tillites – lithified glacial sediments with distinctive textures from past glaciers support the theory of plate tectonics and significant past glacial events.

Deserts & Wind Action

Deserts are areas receiving less than 25 cm of precipitation annually.
Dominant shaping force here is running water (during infrequent heavy rains).
Rare but highly erosive flash floods shape desert landscapes.

Where and How Deserts Form

Dry climate zones (usually where air is descending), caused by patterns and distribution of precipitation, causing arid regions.
Rain-shadow deserts - located downwind of high mountain ranges
Other factors include major weather patterns

Rain Shadow Deserts

Deserts formed downwind from mountain ranges, where the prevalent winds lose their moisture as they rise over the mountains. The air loses moisture as it cools, and then the dry air falls down the other side of the mountain, creating a rain shadow desert effect due to the uneven distribution of precipitation.

Some Characteristics of Deserts

Intermittent streams: streambeds often dry except during brief heavy rains.
Internal drainage: Streams often flow into landlocked basins (no outlet).
Flash floods: common in arid regions due to rapid, intense rainfall events
Desert washes/arroyos: steep-sided, flat-bottomed channels, carrying sediments in occasional high flood events

Desert Features in the Southwestern United States

Two distinct types of landscapes:
- Colorado Plateau, characterized by flat-lying sedimentary rocks that have been eroded into plateaus, mesas and buttes.
- Basin and Range Province, characterized by rugged, linear, fault-bounded mountain ranges, separated by flat valleys. Alluvial fans are common features, formed by merging sediments from canyons during flash floods

Desert Landforms of the Southwestern United States

Alluvial fans – combine to form a bajada as sediments accumulate at the foot of a slope or mountain ranges.
Sediment is transported to valleys

Wind

Larger differences in daily temperatures and pressure create strong wind.
Dust storms, or other atmospheric phenomenon, can transport sediments, such as in the dust bowl of the American and Saharan Desert, across extensive areas.
Volcanic ash can be transported by air.

Wind Erosion and Transportation

Dust can be in suspension but larger sediments (grains) move by saltation.
Wind can effectively "sandblast" rocks to form ventifacts. Deflation (removal of fine particles via wind) causes blowouts and desert pavements.

Wind Deposition: Loess

Loess – wind-blown silt and clay deposited in layers.
Sources – glacial outwash plains, and desert playas.
Forms fertile soils which can be highly eroded.

Wind Deposition: Sand Dunes

Dunes are mounds of loose sand piled up by wind.
Most likely to develop in areas with large sand supplies and constant wind direction.
Different dune types are determined by particular wind conditions and sand supply. The types of sand dunes that form reflect the patterns of wind over time.

Shaping Dunes

Factors that influence dune formation and shape: Wind velocity and direction, Amount of sand, and distribution of vegetation.

Types of Dunes: Barchan

Crescent shaped dunes, with horns that point downwind and a steep slip face on the concave side.
Form in areas with one dominant wind direction and limited sand supply.

Types of Dunes: Transverse

Relatively straight, elongate dunes that develop in areas with large sand supplies and one dominant wind direction.
Long ridges or sheets of sand pile up due to the wind movement and continuous flow.

Types of Dunes: Parabolic

Deeply curved, convex downwind, with horns anchored by vegetation.
Formed around blowouts, common in areas with vegetation.

Types of Dunes: Longitudinal

Long, straight dunes that are parallel to the prevailing wind direction.
Form in regions with large sand supplies.
Mechanism for development is not completely understood.

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Test your knowledge on mass wasting processes and flood management strategies. This quiz covers factors influencing soil stability, types of mass wasting, and the impacts of urbanization and dam construction. Assess your understanding of environmental concerns related to these geological phenomena.