18_groundwater_soil_09_post - 18: Earth’s Resources...

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Unformatted text preview: 18: Earth’s Resources 1-Groundwater • U.S.: Groundwater source of most water used for drinking & irrigation Importance of groundwater Table E.2 • 1% of all water on Earth is groundwater. Springs, Marble Canyon, Grand Canyon National Park, Arizona. • Groundwater volume: 100x greater than lakes / rivers Photo: L. Ulrich Groundwater, Soil: 1 Groundwater, Soil: 2 Groundwater & Water Table Fig. 19.6 Geometry of water table (WT) • WT height mimics ground-surface height. Elevation high, WT high Elevation low, WT low Water table • Unsaturated zone: pore (open) spaces partially filled with water. • Saturated zone: all pore spaces filled with water. • Water table: boundary between the unsaturated zone from the saturated zone • Groundwater: water below water table. Groundwater, Soil: 3 Fig. 19.7 • WT intersects ground surface at flowing streams, marshes, lakes & springs Groundwater, Soil: 4 Groundwater volume Geometry of water table (WT) Elevation of water table changes with amount of precipitation. Fig. 19.2 • Porosity: volume Porosity: of pores in rock or sediment Porosity as cementation packing Wet period sorting Dry period # of fractures Fig. 19.6 Groundwater, Soil: 5 Groundwater, Soil: 6 Controls on groundwater volume Review Questions • Permeability: measure of ease with Permeability: which water moves through ground Porosity: moderate Interconnectedness: none Permeability: none Porosity: high Interconnectedness: high Permeability: high The sketch above that shows three samples of sandstone. The pore spaces (gray) between the sand grains (black) are completely filled in with cement. The long, white features are open fractures (cracks). Q1. Which rock (A, B, or C) has the greatest porosity? Q2. Which rock (A, B, or C) has the lowest porosity? Fig. 19.4 Groundwater, Soil: 7 Porosity: none Permeability: none Q3. Which rock (A, B, or C) has the greatest permeability? Groundwater, Soil: 8 Controls on groundwater volume • Aquifer: porous, permeable unit that holds and releases water • Aquitard: nonporous or nonpermeable unit that does not transmit water Controls on groundwater (GW) flow Groundwater flows from regions of high elevation to low elevation and from regions of high pressure to regions of low pressure Fig. 19.9 Fig. 19.5 • GW may flow down, sideways & up down, Groundwater, Soil: 9 Groundwater, Soil: 10 Review Questions Review Questions 18-1. The majority of liquid fresh water on Earth exists in ____________. A. lakes B. rivers and streams C. pores within rock and sediment D. atmospheric clouds 18-8. Well-sorted sediments typically have ___ porosity compared to poorly sorted sediments. A. greater B. less C. approximately the same 18-2. A. True / B. False: No water is present in the unsaturated zone above the water table. 18-9. Which statement concerning influences on porosity is least correct? A. As the degree of cementation decreases, the porosity increases. B. As the number of fractures increases, the porosity increases. C. As sorting increases, the porosity decreases. D. As the packing of particles increases, the porosity decreases. 18-3. The water table separates: A. an aquifer from an aquiclude B. the unsaturated zone from the saturated zone 18-4. A. True / B. False: The water table is always a flat surface like a table-top. 18-5. The elevation of the water table in a given area is ____________. A. is constant year-round B. may rise during times of drought and sink during rainy periods C. may rise during rainy periods and sink during droughts 18-6. A. True / B. False: Unconsolidated sediment typically has greater porosity than lithified rock which forms from it. 18-7. A. True / B. False: Groundwater only flows downward. Groundwater, Soil: 11 18-10. A. True / B. False: If the porosity of a rock is high, the permeability must also be high. 18-11. A. True / B. False: If the permeability of a rock is high, the porosity must also be high. 18-12. A. True / B. False: The relative height of the water table decreases under hills and increases under valleys. 18-13. A. True / B. False: Swamps and lakes are regions where the water table lies at the Earth’s surface. Groundwater, Soil: 12 Springs and wells Springs and wells • Spring: water issuing from the ground, marking a place Spring: where the water table intersects the Earth’s surface Earth’ Fig. 19.13 • Well: hole drilled Well: below water table from which water is pumped to surface. • Cone of depression: depression: depression of the water table produced by pumping Thousand springs, Snake River Canyon, Idaho. Groundwater, Soil: 13 Photo: W.K. Hamblin Well-extraction problems Groundwater, Soil: 14 Well-extraction problems • Water removed from aquifer may cause particle compaction --> ground subsidence & fissures. Fig. 19.21 Leaning tower of Pisa & Venice, Italy Photos: R.W. Schlische Fig. 19.21 Groundwater, Soil: 15 Also: New Orleans Groundwater, Soil: 16 Well-extraction problems Well-extraction problems • Excessive pumping --> shallow wells may run dry Fig. 19.21 • Saltwater encroachment: encroachment: pumping of freshwater (which lies above heavier saltwater) may cause saltwater to move toward the well Groundwater, Soil: 17 Groundwater activity • Caves: enlarged solution cavities produced when acidic groundwater Caves: dissolves calcite from regions underlain by limestone and marble Cave deposits in Luray Caverns, Luray, VA. Photo: R.W. Schlische Groundwater, Soil: 19 1 3 Fig. 19.13 2 Groundwater, Soil: 18 Caves • Caves form below water table (WT) • Cave deposits form when water table drops Fig. 19.30 Groundwater, Soil: 20 Groundwater activity: cave deposits Groundwater activity • Sinkhole: surface depression formed by the collapse of the roof of a cave Sinkhole: See Fig. 19.1, 19.29 Fig. 19.28 • Stalactite: deposit of calcite that forms on the ceiling of a cave as water evaporates and precipitates calcite. • Stalagmite: deposit of calcite on the ground of a cave produced by evaporating groundwater that has dripped down from above. • Column: produced when a stalactite and stalagmite grow toward each other. Groundwater, Soil: 21 Sinkhole in Winter Park, Florida. Photo: L. Skoogfors Groundwater, Soil: 22 Groundwater activity Karst topography Sinkholes Plate, p. 682 Fig. 19.29 • Karst topography: region topography: underlain by limestone (or marble) characterized by sinkholes and disappearing streams Groundwater, Soil: 23 Disappearing stream in China. Photo: W.K. Hamblin Groundwater, Soil: 24 Soil Formation Review Questions 18-14. Nonrenewable use of groundwater refers to situations where the removal of groundwater exceeds the replenishment of groundwater. Land subsidence is likely whenever ____________. A. groundwater is used nonrenewably from aquifers composed of rock B. groundwater is used nonrenewably from aquifers composed of sediment 18-15. Which of the following is not a cave deposit? A. sinkhole B. column C. stalagmite D. stalactite 18-16. Which of the following cave deposits only grow down from the roof of a cave? A. column B. stalactite C. stalagmite Soil: loose weathered rock with organic matter that can support vegetation. 18-17. Most dissolution of bedrock to form caves takes place ____________. A. above the water table B. below the water table 18-18. A. True / B. False: Most cave deposits form when the cave is located below the water table. 18-19. Sinkholes are a concern in areas where the bedrock is ____________. A. sandstone B. shale C. limestone D. granite Fig. 7.12b 18-20. Topography dominated by sinkholes is termed ____________. A. valley and ridge B. karst C. horst and graben Groundwater, Soil: 25 Fig. 7.13a Groundwater, Soil: 26 Soil horizons Soil-forming factors • Bedrock composition: thicker soil on more easily weathered rocks Photo: Dept. of Primary Industries, Victoria, Australia Groundwater, Soil: 27 Soil profile: distinctive layers (horizons) within a soil 1. O horizon: top horizon consisting mostly of decomposing organic matter. 2. A horizon: zone of leaching of soluble material. 3. B horizon: zone of accumulation of soluble material. 4. C horizon: partially weathered bedrock. Fig. 7.13 Groundwater, Soil: 28 Soil-forming factors • Slope: thicker soils on gentler slopes Fig. 7.13 Soil-forming factors • Time: thicker soil after more weathering Fig. 7.13 Groundwater, Soil: 29 Groundwater, Soil: 30 Soil-forming factors Soils: Mineral Resources Soils are better developed in humid regions (tropical & temperate) Fig. 7.14d In tropical settings, the most soluble minerals are leached out of the A-horizon, leaving behind iron-rich deposits (laterite) and aluminum-rich deposits (bauxite) Fig. 7.14c Groundwater, Soil: 31 Groundwater, Soil: 32 Review Questions 18-21. Which soil horizon is the zone of accumulation, so named because dissolved matter, leached from other parts of the soil, precipitates to form new minerals. A. A-horizon B. B-horizon C. C-horizon D . O-horizon 18-22. Which soil horizon is chemically most similar to the underlying bedrock or unaltered sediment? A. A-horizon B. B-horizon C. C-horizon D. O-horizon 18-23. Which soil horizon has the greatest proportion of organic matter? A. A-horizon B. B-horizon C. C-horizon D. O-horizon 18-24. The shallowest soil horizon is: A. A horizon B. B horizon C. C horizon D. O horizon 18-25. A. True / B. False: Soils are thickest in humid regions and on gentle slopes. 18-26. Laterite soils are most commonly found in which type of environments? A. temperate forests B. tropical rain forests C. deserts D. grasslands Groundwater, Soil: 33 ...
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This note was uploaded on 09/25/2011 for the course GEOLOGY 100 taught by Professor Lepre during the Fall '11 term at Rutgers.

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