Landform Geography

Groundwater and

Karst Landscapes

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

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

Karst Landforms

• Caves, sinkholes and other soluble rock features

• Form in extensive, thick deposits of limestone

• Limestone 80%+ calcium carbonate – dissolves easily through carbonation

Caves and Caverns• Caves – underground

voids in rock big enough for people to enter

• Cavern – large cave system

• Form just below water table in limestone – when

water table falls, empty caverns are exposed

Karst Topography - Sinkholes

• Most common surface feature of karst is sinkhole

• Sinkhole – depression in regions of cavernous limestone – forms from collapse of cave

• Often found with disappearing streams that enter underground channels

• Some sinkholes fill with water, forming ponds

• Sinkholes can be hazards, collapsing under homes or roads

Sinkhole Landscape