Post on 22-Dec-2015
Water Under the GroundWater Under the Ground
Chapter 12
Water On and Under the Ground
Geology Today
Barbara W. Murck
Brian J. Skinner
N. Lindsley-Griffin, 1999
Lutgens & Tarbuck, J.R. Griffin, 1999
Carlsbad Caverns, NM
The Water TableThe Water Table Water Table = Top surface
of the saturated zone Zone of aeration (unsaturated zone) - pores filled with air
Saturated zone - pores filled with water
N. Lindsley-Griffin, 1999
Fig. 12.22
p. 353
How Groundwater MovesHow Groundwater Moves
N. Lindsley-Griffin, 1999Fig. 12.24, p. 355
N. Lindsley-Griffin, 1999
A stream that lies above the water table loses water to the zone of saturation, will dry up at times.
A stream that lies below the water table receives water from zone of saturation, will flow all year.
Groundwater and StreamsGroundwater and Streams
Porosity and PermeabilityPorosity and PermeabilityPorosity - percentage of total volume of rock that consists of open spaces (pores). (how many pores, and how big they are)
Permeability - a measure of how easily a solid allows fluids to pass through it. (how well connected the pores are)
N. Lindsley-Griffin, 1999
Fig. 12.23
p. 354
Porosity and PermeabilityPorosity and Permeability
IN GENERAL -
Porosity and permeability
are better in:
well sorted sediments
loosely packed sediments
spherical sediments
Cementation of sediment decreases both porosity and permeability
N. Lindsley-Griffin, 1999
Low Porosity High Porosity
Poorly sorted Well sorted
Tightly packed Loosely packed
Nonspherical Spherical
AquifersAquifersAquifer - a body of water-saturated, porous and permeable, rock or regolith
N. Lindsley-Griffin, 1999
Fig. 12.26
p. 358
AquifersAquifers
Confined aquifer: trapped between impermeable layers (aquicludes).
Unconfined aquifer: top of saturation zone is water table
N. Lindsley-Griffin, 1999 Fig. 12.26, p. 358
RechargeRecharge Recharge - replenishment of groundwater
Recharge zone - where groundwater is replenished by infiltration of rainfall and snowfall, which percolates downward to the saturated zone.
N. Lindsley-Griffin, 1999
Fig. 12.26, p. 358
DischargeDischarge Discharge - process by which groundwater returns to the surface.
Examples: streams, springs, wells, the ocean.
N. Lindsley-Griffin, 1999
WellsWells Pumping produces a cone of depression in the water table around the well.
Fig. 12.29, p. 360
N. Lindsley-Griffin, 1999
ArtesianWellsArtesianWellsArtesian system: water pushed up to
water table by hydraulic pressure.
Requires a confined aquifer, and sufficient pressure.
Usually supplied by folded or faulted beds that surface at a higher elevation in the recharge area.
N. Lindsley-Griffin, 1999
Fig. 12.27
p. 359
Sources of Groundwater ContaminationSources of Groundwater Contamination
Leaching of toxic chemicals from unlined landfills.
Leaking septic tanks. Agricultural chemicals.
LUST (Leaking Underground Storage Tanks)
N. Lindsley-Griffin, 1999
Fig.12.30, p. 361
SpringsSprings
Springs form where a change in rock permeability forces groundwater out to the surface: a) limestone over shale.
N. Lindsley-Griffin, 1999Fig. 12.28, p. 359
SpringsSprings Springs form…
b) highly jointed permeable rock like a lava flow over impermeable limestone, or c) along a fault.
N. Lindsley-Griffin, 1999Fig. 12.28, p. 359
SpringsSprings
Springs form…
c) along a fault,
- where a permeable layer is blocked by being moved against an impermeable layer,
- or where the fault itself is impermeable.
N. Lindsley-Griffin, 1999Fig. 9.11, p. 251
Caves and Caverns
Caves and Caverns
Caves and caverns - underground open spaces - form by dissolution of carbonate rocks near the top of a seasonally fluctuating water table.
They are closed to the surface or have only a small opening.
Fig. 12.25 B, p. 357 N. Lindsley-Griffin, 1999
Caves and CavernsCaves and Caverns
Underground cavities form when water table is high, then fill with air when water table drops and water drains out.
Houghton Mifflin, 1998; N. Lindsley-Griffin, 1999
Earlierwatertable
Presentwatertable
Caves and CavernsCaves and Caverns
After water table drops, percolation of acidic water from the surface dissolves ions which precipitate as calcite cave decorations in the open air of the cave.
Houghton Mifflin, 1998; N. Lindsley-Griffin, 1999
Earlierwatertable
Presentwatertable
SinkholesSinkholes Sinkholes are dissolution cavities that are open to the sky. They form
by collapse of cave roofs or where rainwater is rich in carbon dioxide
N. Lindsley-Griffin, 1999
Winter Park sinkhole, near Orlando FL - May 8-9, 1981
Grew to >100 m wide in 17 hours.
Fig. 12.25 C, p. 357
KarstKarstExtensive dissolution produces karst topography, with many small closed basins and sinkholes, and disrupted drainage.
(Fig. 12.25A, p. 356)
N. Lindsley-Griffin, 1999
KarstKarstProlonged development of karst results in topography with jagged carbonate towers that served as the inspiration for Chinese scroll painting.
Houghton Mifflin, 1998; N. Lindsley-Griffin, 1999
Limestone towers
Auilin, China
Cave - a natural cavity below
Earth’s surface
• Caves in limestone form by dissolution...
• below the water table.
N. Lindsley-Griffin, 1998
“Soda Straws”
Cave decorations form by
precipitation above the water table
Sinkholes form when a cave roof collapses
FossilizationFossilizationGroundwater aids fossilization by leaching away organic matter and depositing silica or carbonate ions
Houghton Mifflin, 1998; N. Lindsley-Griffin, 1999
Petrified Forest, AZ
Hot Springs and GeysersHot Springs and Geysers
Hot springs form where groundwater heated by subsurface magma rises to the surface.
Geysers (1) are eruptions of hot water caused when groundwater confined in subsurface fissures becomes superheated.
Houghton Mifflin, 1998; N. Lindsley-Griffin, 1999
N. Lindsley-Griffin, 1999
Hot Springs and GeysersHot Springs and Geysers
Geysers (2) Superheated water at depth expands, causing water to slop over the rim and releasing the confining pressure.
(3) Water “flashes” into
steam and the geyser erupts.
Hot spring deposits form by precipitation of dissolved ions as
the water cools