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Unformatted text preview: GEOGRAPHY 121 FINAL EXAM Chapter 16: Underground Water and Karst Landforms- Earth’s fresh water resources are very limited o 70% is stored as glacier ice in polar regions o 30% is underground- Underground Water System in Humid Regions (Figure 16.2) o Primary Inputs: precipitation and snowmelt infiltrating the ground o Major Output (outflow) occurs through dug wells/natural springs o Percolation: process by which water drains downward by gravity beyond the zone of aeration to lower levels o Subsurface Water System has Three Layers Zone of Aeration Intermediate Zone Zone of Saturation: • Water occupies all of the void spaces in this zone - groundwater • Top of zone of saturation is the water table • Water table dept is dependant on changes in infiltration and outflow, falling during dry seasons and rising during wet seasons • Water table is the surface of the zone of saturation through which water flows towards a nearby river - Aquifer : a natural underground storage medium for groundwater. o When impermeable rock exists below an aquifer a perched water table can form because the downward percolating soil water was prevented from reaching the zone of saturation o A sequence of porous and permeable layers of sediments of rock that act as a storage medium and transmitter of water Sandstones, limestone, loose coarse sediments o- Pumping of water from wells may cause the development of cones of depression – adjacent cones of depression can lower the regional water table causing shallow wells to become dry o Wells are artificial openings dug or dilled below the water table to extract water - Principal Role of subsurface water in landform development is to encourage mass movement by adding weight and reducing strength of soil/sediments - Limestone is the most common soluble rock – wherever water can act on a rock type that’s soluble in water, a distinctive landscape will develop- Karst Landforms – landforms developed dominantly by solution, named after the Karst Plateau along Croatia o Necessary Circumstances for development of Karst Landscape Warm humid climate with ample precipitation Presence of carbon dioxide from vegetation – warmer climates Active movement of subsurface water - Sinkholes: roughly circular surface depressions developed by concentrated solution; prominent feature of karst landscapes - Figure 6.10 – distribution of limestone in the US o High concentrations in Florida, Texas, just west of the Mississippi- Groundwater flowing along joints and bedding planes below the surface can dissolve limestone sometimes creating a system of connected passageways within soluble bedrock - if the water table falls and these passageways are above the zone of saturation this is called a cave o Caverns develop along zones of weakness and groundwater flow widens (limestone) fractures to develop a cave system - Karst Topography o Florida’s central lake region is a good place to study karst topography because its surface and subsurface show effects of subsurface water,...
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This document was uploaded on 10/27/2011 for the course GEO 121 at Miami University.
- Fall '08