Landform Geography

Lecture 5

Mass Wasting Events

Groundwater

Mass Wasting• Large volumes of sediment moving down hill

slopes under force of gravity

• Types:

Solifluction• Form of soil creep in tundra landscapes

• Surface of permafrost melts & soil sags down slope in uneven lobes

Earth Flow

• Slow-to-rapid movement of wet soil & other loose sediment over a broad surface

• One of 3 types of Flow – mass movement of wet sediment

Mudflow• Fine textured sediments that move very quickly

down slope – occur after heavy rainfall

• Lahar – Indonesian word for volcanic mudflow

Debris Flow• Mud, boulders, trees, etc. flowing down

slope after heavy rainfall – very dangerous

La Conchita, CADebris Flow

Slump• Slide where rock & sediment rotates & moves

down slope along plane concave to surface

• Happens on slopes w/ soft deposits rich in clay and shale

Debris Slide• Type of Landslide – mass of rock, regolith &

soil that flows downhill• Slope failure along a plane roughly parallel to

the slope

Madison Slide,Montana

Soil Creep• Slowest mass wasting process

• Force of gravity slowly pulls soil particles down hill – features of hill shift down hill, as well

Rockfall

• Process in which rocks break free from cliff faces & rapidly tumble into valley below

Avalanche• Large mass of snow or rock that suddenly slides

down a mountainside

Weathering and Mass Movements

Groundwater and Karst Landscapes

• Movement & Storage of groundwater– High Plains aquifer

– Subsidence

– Groundwater contamination

• Karst Landforms & Landscapes– Caves & Caverns

– Karst topography

Movement & Storage of Groundwater

• Precipitation sinks into soil’s soil-water belt

• In dry soil, water is held tight by sediment grains as hygroscopic water – unavailable for plants

• When pore spaces within soil full of water, soil at Field Capacity – additional water flows down into unsaturated zone

• Water collects above an impermeable aquiclude to form saturated zone

• Large saturated zone is aquifer

Fate of Precipitation on Soil

Soil-Water Conditions

Saturated Zones & Aquicludes

Hydrologic Cycle and Groundwater

High Plains (Ogallala) Aquifer• Underlies much of

Great Plains from TX to SD

• Water deposited in Ice Ages 1.6 M-10K yrs ago

• Heavy usage, esp. center-pivot irrigation

• Drawdown significant in parts of aquifer

High Plains (Ogallala) Aquifer

Center-Pivot Irrigation Drawdown

Artesian Wells and Springs• Natural pressure brings water to surface in

artesian well

Patterns of Groundwater Depletion• Cone of Depression – cone-shaped depression in

water table that occurs around a well

Subsidence

• Settling or sinking of a surface due to removal of water or sediment from below

• Worst around large cities such as Venice, Italy and agricultural regions such as the San Joaquin Valley of California

Groundwater Contamination• Dumped chemicals can be carried by moving

groundwater to sources of drinking water

• Recent federal rules have reduced uncontrolled dumping and contamination