Geology Study Guide: Mass Wasting, Water, Glaciers & Deserts

Exam 4

Mass wasting

Downhill movement of rock, soil, and debris under gravity

Main cause of mass wasting

Gravity;often aided by weathering and water.

When mass wasting occurs

When gravitational force > resisting force (shear strength).

Slope angle

Steeper = less stable.

Water content

Adds weight, reduces friction

Vegetation

Roots stabilize slopes; removal increases risk.

Weathering & climate

Weakens rock; humid areas more prone.

Overloading

Extra weight from fill, buildings or snow

Geologic structure

Slopes parallel to rock layers are more unstable.

Triggers of mass wasting

Earthquakes, heavy rain, volcanic eruptions, snowmelt

Rockfall

Free fall of rock; very fast

Slump

Curved surface rotation of soil/debris; moderate speed.

Rockslide

Planar movement of rock; very fast

Mudflow

Flow with high water of silt/clay; very fast

Debris flow

Flow with less water of coarse debris; fast

Earthflow

Flow of wet soil; slow

Creep

Flow of soil; very slow

Solifluction

Flow in permafrost of saturated soil; slow

Cut-and-fill method

Remove upper slope, use as base fill.

Benching

Step-like cuts into slope.

Drainage improvement

Reduces weight and water pressure.

Gradient

Slope measured in meters per kilometer (m/km).

Velocity

Speed of flow; faster in deeper/central parts.

Discharge

Volume per time measured in cubic meters per second (m³/s).

Discharge formula

Discharge = width × depth × velocity.

Dissolved load

Ions in solution carried by water.

Suspended load

Fine particles (silt, clay) kept in motion by tubulence.

Bed load

Sand, gravel moving by rolling, sliding, or bouncing (saltation).

Braided streams

Multiple channels; sediment supply > transport capacity.

Meandering streams

Single, curving channel; erosion at cut bank, deposition at point bar.

Oxbow lake

Formed when a meander is cut off.

Floodplains

Flat areas beside rivers that flood often.

Natural levees

Built-up ridges along riverbanks.

Deltas

Sediment deposited where rivers meet standing water.

Alluvial fans

Cone-shaped deposits in arid regions at mountain bases.

Flood control structures

Dams, levees, floodwalls, floodways.

Drainage patterns

Dendritic (tree-like), Rectangular (faulted areas), Trellis (folded terrain), Radial (volcanoes), Deranged (glacial).

Downcutting

Process that deepens a valley.

Lateral erosion

Process that widens a valley.

Headward erosion

Lengthens valley.

Stream terraces

Old floodplains left above current level.

Incised meanders

Meanders cut into bedrock after uplift.

Groundwater

Water stored in pores and fractures below Earth's surface (~0.6% of all water).

Porosity

% of material that is pore space (how much water can be held).

Permeability

Ability to transmit water through connected pores.

Zone of aeration

Above water table; contains air and water.

Zone of saturation

Below water table; all pores filled with water.

Water table

Boundary between the two zones; rises after rain; falls in drought.

Recharge

Rain, snowmelt entering ground

Aquifer

Rock/sediment layer that transmits water easily (sandstone, gravel)

Aquiclude

Impermeable layer (shale, granite)

Artesian well

Water rises naturally due to pressure between two aquicludes.

Karst topography

From groundwater dissolving limestone.

Overpumping

Lowers water table (cone of depression).

Saltwater intrusion

Near coasts.

Pollution

Chemicals

Subsidence

Ground sinks as water is removed.

Hot springs

Water heated by magma rises to surface.

Geysers

Intermittent eruptions caused by pressure buildup in underground chambers.

Geothermal Energy

Uses Earth's internal heat to produce power renewable and clean alternative to fossil fuels.

Glacier

Large mass of moving ice formed from compacted snow.

Valley (alpine) glaciers

In mountain valleys.

Continental glaciers

Cover broad regions (Greenland

Plastic flow

Internal deformation under pressure.

Basal slip

Entire ice mass slides over bedrock.

Plucking

Ice lifts rocks.

Abrasion

Rock fragments grind surface.

Striations

Grooves scratched into bedrock.

Dunes

Mounds of sand formed by wind  shape depends on wind direction and sand supply.

Loess

Fine silt/clay deposited by wind forms fertile soils.

Deserts

Areas receiving

Mechanical weathering

Dominant (frost wedging,thermal expansion).

Flash floods

Main agent of erosion.

Wind erosion

Important where vegetation is sparse.

Desert pavement

Surface of closely packed pebbles from wind removing fine particles.