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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
• 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
of pores in rock or
sediment Porosity as cementation
Wet period sorting Dry period # of fractures
Groundwater, Soil: 5 Groundwater, Soil: 6 Controls on groundwater volume Review Questions • Permeability: measure of ease with
which water moves through ground Porosity: moderate
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
Groundwater, Soil: 9 Groundwater, Soil: 10 Review Questions Review Questions 18-1. The majority of liquid fresh water on Earth exists in ____________.
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.
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
18-11. A. True / B. False: If the permeability of a rock is high, the porosity must also
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
where the water table intersects the Earth’s surface
Earth’ Fig. 19.13
• Well: hole drilled
below water table from
which water is pumped
to surface. • Cone of depression:
depression of the
water table produced
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
well Groundwater, Soil: 17 Groundwater activity
• Caves: enlarged solution cavities produced when acidic groundwater
dissolves calcite from regions underlain by limestone and marble Cave deposits
VA. Photo: R.W.
Schlische Groundwater, Soil: 19 1 3 Fig. 19.13
2 Groundwater, Soil: 18 Caves
• Caves form
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
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
underlain by limestone (or
marble) characterized by
sinkholes and disappearing
Groundwater, Soil: 23 Disappearing stream in
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
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?
C. stalagmite D. stalactite 18-16. Which of the following cave deposits only grow down from the roof of a cave?
C. stalagmite Soil: loose
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
18-19. Sinkholes are a concern in areas where the bedrock is ____________.
D. granite Fig. 7.12b 18-20. Topography dominated by sinkholes is termed ____________.
A. valley and ridge
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
leached out of the
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.
D . O-horizon
18-22. Which soil horizon is chemically most similar to the underlying bedrock or
18-23. Which soil horizon has the greatest proportion of organic matter?
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
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.
- Fall '11