Post on 27-Dec-2015
transcript
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