EXPLANATION and carbonate- · 2001. 12. 4. · JDJDJDJDJD 0 10 20 422 420 418 416 414 412 410 408...
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A14 SANDSTONE AND CARBONATE- ROCK AQUIFERS Aquifers in sandstone and carbonate rocks are most wide- spread in the eastern half of the Nation, but also extend over large areas of Texas and smaller areas in Oklahoma, Arkan- sas, Montana, Wyoming, and South Dakota (fig. 4). These aquifers consist of interbedded sandstone and carbonate rocks; the carbonate rocks are the most productive aquifers, whereas the interbedded sandstones yield less water. The aquifers in the Mammoth Cave area of Kentucky are examples of sand- stone and carbonate-rock aquifers. The development of solu- tion openings and karst topography in the limestones of the Mammoth Cave area are discussed in the preceding section of this report; the following section discusses the relations of the sandstone and carbonate-rock aquifers in that area. Movement of water through the unconfined and confined parts of the limestone aquifers that underlie the Pennyroyal Plain and Mammoth Cave Plateau is summarized in figure 38. Where the St. Louis Limestone is exposed at the land surface in the Pennyroyal Plain, water from surface streams enters un- derground solution cavities through swallow holes and sink- holes. Water also enters solution cavities in the Ste. Genevieve and Girkin Limestones through sinkholes that have developed in the Big Clifty Sandstone Member of the Golconda Forma- tion that caps the Mammoth Cave Plateau. The sinkholes on the plateau are collapse sinkholes that developed when the sandstone cap collapsed into caves which formed in the un- derlying limestone. Many of the solution openings in the Girkin and Ste. Genevieve Limestones are dry because they formed when the erosional base level in the area was at a higher alti- tude. Water from the saturated solution openings in the Ste. Genevieve and St. Louis Limestones discharges to the Green River from springs in the river channel and valley walls. Large quantities of water move rapidly to the river through the solu- tion openings. Water moves slowly through intergranular pore spaces and small fractures in the Big Clifty Sandstone Member of the Golconda Formation. Discontinuous layers of shale in the un- derlying Girkin Limestone (fig. 38) impede the downward movement of water and create a perched water table from which small springs discharge at the escarpments bounding the Mammoth Cave Plateau. The presence or absence of solution openings affects aquifer recharge and discharge and is reflected by the water levels in wells completed in different rock types. The water level in well A (fig. 39A), completed in the Big Clifty Sand- stone Member of the Golconda Formation (fig. 38), rises quickly in response to seasonal increases in precipitation; after the sudden rise, the water slowly drains from the aquifer and the water level declines slowly. In contrast, the water level in well B (fig. 39B), which is open to the St. Louis and Ste. Genevieve Limestones, rises sharply only in response to heavy rains. Following the abrupt rise, the water level in this well declines quickly as the solution cavities penetrated by the well are drained. The large openings allow rapid recharge and equally rapid discharge during and immediately following periods of intense precipitation. The transmissivity (rate at which water moves through an aquifer) of the part of the rock that contains solution openings is extremely high, whereas that of the undissolved rock between the solution conduits gener- ally is very low. BASALTIC- AND OTHER VOLCANIC-ROCK AQUIFERS Aquifers in basaltic and other volcanic rocks are wide- spread in Washington, Oregon, Idaho, and Hawaii, and extend over smaller areas in California, Nevada, and Wyoming (fig. 4). Volcanic rocks have a wide range of chemical, mineralogic, structural, and hydraulic properties. The variability of these properties is due largely to rock type and the way the rock was ejected and deposited. Pyroclastic rocks, such as tuff and ash deposits, might be emplaced by flowage of a turbulent mix- ture of gas and pyroclastic material, or might form as wind- blown deposits of fine-grained ash. Where they are unaltered, pyroclastic deposits have porosity and permeability charac- teristics like those of poorly sorted sediments; where the rock fragments are very hot as they settle, however, the pyroclas- tic material might become welded and almost impermeable. Silicic lavas, such as rhyolite or dacite, tend to be extruded as thick, dense flows and have low permeability except where they are fractured. Basaltic lavas tend to be fluid and form thin flows that have a considerable amount of primary pore space at the tops and bottoms of the flows. Numerous basalt flows commonly overlap and the flows commonly are separated by soil zones or alluvial material that form permeable zones. Basalts are the most productive aquifers of all volcanic rock types. The permeability of basaltic rocks is highly variable and depends largely on the following factors: the cooling rate of the basaltic lava flow, the number and character of interflow zones, and the thickness of the flow. The cooling rate is most rapid when a basaltic lava flow enters water. The rapid cool- ing results in pillow basalt (fig. 40), in which ball-shaped masses of basalt form, with numerous interconnected open spaces at the tops and bottoms of the balls. Large springs that discharge thousands of gallons per minute issue from pillow basalt in the wall of the Snake River Canyon at Thousand Springs, Idaho. Interflow zones are permeable zones that de- velop at the tops and bottoms of basalt flows (fig. 41). Frac- tures and joints develop in the upper and lower parts of each flow, as the top and bottom of the flow cool while the center of the flow remains fluid and continues to move, and some vesicles that result from escaping gases develop at the top of the flow. Few open spaces develop in the center of the flow because it cools slowly. Thus, the flow center forms a dense, low-permeability zone between two more permeable zones. Thin flows cool more quickly than thick flows, and accordingly the centers of thin flows commonly are broken and vesicular like the tops and bottoms of the flows. The Snake River Plain regional aquifer system in south- ern Idaho and southeastern Oregon (fig. 42) is an example of an aquifer system in basaltic rocks. The Snake River Plain is a large graben-like structure that is filled with basalt of Mi- ocene and younger age (fig. 43). The basalt consists of a large number of flows, the youngest of which was extruded about 2,000 years ago. The maximum thickness of the basalt, as es- timated by using electrical resistivity surveys, is about 5,500 feet. The basalt is bounded at the margins of the plain by si- licic volcanic and intrusive rocks that are downwarped toward the plain. NOT TO SCALE Chattanooga Shale Warsaw Limestone and Fort Payne Formation St Louis Limestone Ste Genevieve Limestone Girkin Limestone Green River Big Clifty Sandstone Member of Golconda Formation Sinkhole Sinkhole Sinkhole Swallow hole Perched water table Well A Well B Spring Spring NW SE Mammoth Cave Plateau Pennyroyal Plain Water table 37° 39° 83° 85° 87° 89° K E N T U C K Y Mammoth Cave Plateau Mammoth Cave Area Pennyroyal Plain 1953 1954 1955 1956 1957 J DJ DJ DJ DJ D 0 10 20 422 420 418 416 414 412 410 408 406 20 18 16 14 12 10 8 6 4 2 0 PRECIPITATION, IN INCHES WATER LEVEL, IN FEET BELOW LAND SURFACE A B Well Well Flow top– vesicular, scoriaceous and broken; substantial permeability Flow center– dense, few vesicles, most fractures are vertical; mini- mal permeability Flow bottom– vesicular and broken; substan- tial permeability Modified from Whitehead, 1992 Base modified from U.S. Geological Survey digital data, 1:2,000,000, 1972 Modified from Whitehead, 1992 ■ Thousand Springs W A S H I N G T O N O R E G O N I D A H O S n a k e R i v e r S n a k e R i v e r C o lu m b i a River C o l u m b i a R i v e r P a c i f i c O c e a n 120° 115° 48° 43° ● ● ● ● Seattle Spokane Olympia Portland Salem Eugene Boise Pocatello ● ★ ★ ★ Yellowstone National Park EXPLANATION Direction of ground-water movement EXPLANATION Snake River Plain regional aquifer system Figure 38. Large volumes of water move rapidly from sinkholes and swallow holes through a well-developed net- work of solution cavities in the St. Louis and Ste. Genevieve Limestones to discharge at springs or to the Green River. The openings were formed by dissolution of the limestones as water moved along bedding planes and fractures. Figure 39. Water levels in wells completed in sandstone and carbonate-rock aquifers respond differently to recharge. Changes in the water level in well A, completed in sandstone, show that the sandstone is recharged quickly but drains slowly. In contrast, changes in the water level in well B, open to underlying limestone formations, show that recharge to and discharge from the carbonate-rock aquifer are rapid due to large solution openings in the limestone. Figure 40. Pillow basalt forms when basaltic lava enters water and cools quickly. Extensive interconnected pore spaces develop in the flow as the ball-shaped pillows cool. Figure 41. A typical basalt flow contains zones of varying permeability. Vesicular, broken zones at the top and bottom of the flow are highly permeable, whereas the dense center of the flow has minimal permeability. Figure 42. The Snake River Plain, which is located in southern Idaho and southeastern Oregon, is underlain by basalt aquifers. Sandstone and carbonate- rock aquifers Basaltic and other Volcanic–rock aquifers Modified from Brown, 1966; and Quinlan and others, 1983 Modified from Brown, 1966 R.L. Whitehead 1980 0 50 25 MILES 0 50 25 KILOMETERS SCALE 1:7,500,000
Transcript of EXPLANATION and carbonate- · 2001. 12. 4. · JDJDJDJDJD 0 10 20 422 420 418 416 414 412 410 408...
A14
SANDSTONE AND CARBONATE-ROCK AQUIFERS
Aquifers in sandstone and carbonate rocks are most wide-spread in the eastern half of the Nation, but also extend overlarge areas of Texas and smaller areas in Oklahoma, Arkan-sas, Montana, Wyoming, and South Dakota (fig. 4). Theseaquifers consist of interbedded sandstone and carbonate rocks;the carbonate rocks are the most productive aquifers, whereasthe interbedded sandstones yield less water. The aquifers inthe Mammoth Cave area of Kentucky are examples of sand-stone and carbonate-rock aquifers. The development of solu-tion openings and karst topography in the limestones of theMammoth Cave area are discussed in the preceding sectionof this report; the following section discusses the relations ofthe sandstone and carbonate-rock aquifers in that area.
Movement of water through the unconfined and confinedparts of the limestone aquifers that underlie the PennyroyalPlain and Mammoth Cave Plateau is summarized in figure 38.Where the St. Louis Limestone is exposed at the land surface
in the Pennyroyal Plain, water from surface streams enters un-derground solution cavities through swallow holes and sink-holes. Water also enters solution cavities in the Ste. Genevieveand Girkin Limestones through sinkholes that have developedin the Big Clifty Sandstone Member of the Golconda Forma-tion that caps the Mammoth Cave Plateau. The sinkholes onthe plateau are collapse sinkholes that developed when thesandstone cap collapsed into caves which formed in the un-derlying limestone. Many of the solution openings in the Girkinand Ste. Genevieve Limestones are dry because they formedwhen the erosional base level in the area was at a higher alti-tude. Water from the saturated solution openings in the Ste.Genevieve and St. Louis Limestones discharges to the GreenRiver from springs in the river channel and valley walls. Largequantities of water move rapidly to the river through the solu-tion openings.
Water moves slowly through intergranular pore spacesand small fractures in the Big Clifty Sandstone Member of theGolconda Formation. Discontinuous layers of shale in the un-derlying Girkin Limestone (fig. 38) impede the downwardmovement of water and create a perched water table from
which small springs discharge at the escarpments boundingthe Mammoth Cave Plateau.
The presence or absence of solution openings affectsaquifer recharge and discharge and is reflected by the waterlevels in wells completed in different rock types. The waterlevel in well A (fig. 39A), completed in the Big Clifty Sand-stone Member of the Golconda Formation (fig. 38), risesquickly in response to seasonal increases in precipitation; afterthe sudden rise, the water slowly drains from the aquifer andthe water level declines slowly. In contrast, the water level inwell B (fig. 39B), which is open to the St. Louis and Ste.Genevieve Limestones, rises sharply only in response to heavyrains. Following the abrupt rise, the water level in this welldeclines quickly as the solution cavities penetrated by the wellare drained. The large openings allow rapid recharge andequally rapid discharge during and immediately followingperiods of intense precipitation. The transmissivity (rate atwhich water moves through an aquifer) of the part of the rockthat contains solution openings is extremely high, whereas thatof the undissolved rock between the solution conduits gener-ally is very low.
BASALTIC- AND OTHERVOLCANIC-ROCK AQUIFERS
Aquifers in basaltic and other volcanic rocks are wide-spread in Washington, Oregon, Idaho, and Hawaii, and extendover smaller areas in California, Nevada, and Wyoming (fig.4). Volcanic rocks have a wide range of chemical, mineralogic,structural, and hydraulic properties. The variability of theseproperties is due largely to rock type and the way the rock wasejected and deposited. Pyroclastic rocks, such as tuff and ashdeposits, might be emplaced by flowage of a turbulent mix-ture of gas and pyroclastic material, or might form as wind-blown deposits of fine-grained ash. Where they are unaltered,pyroclastic deposits have porosity and permeability charac-teristics like those of poorly sorted sediments; where the rockfragments are very hot as they settle, however, the pyroclas-tic material might become welded and almost impermeable.Silicic lavas, such as rhyolite or dacite, tend to be extrudedas thick, dense flows and have low permeability except wherethey are fractured. Basaltic lavas tend to be fluid and form thinflows that have a considerable amount of primary pore spaceat the tops and bottoms of the flows. Numerous basalt flowscommonly overlap and the flows commonly are separated bysoil zones or alluvial material that form permeable zones.Basalts are the most productive aquifers of all volcanic rocktypes.
The permeability of basaltic rocks is highly variable anddepends largely on the following factors: the cooling rate ofthe basaltic lava flow, the number and character of interflow
zones, and the thickness of the flow. The cooling rate is mostrapid when a basaltic lava flow enters water. The rapid cool-ing results in pillow basalt (fig. 40), in which ball-shapedmasses of basalt form, with numerous interconnected openspaces at the tops and bottoms of the balls. Large springs thatdischarge thousands of gallons per minute issue from pillowbasalt in the wall of the Snake River Canyon at ThousandSprings, Idaho. Interflow zones are permeable zones that de-velop at the tops and bottoms of basalt flows (fig. 41). Frac-tures and joints develop in the upper and lower parts of eachflow, as the top and bottom of the flow cool while the centerof the flow remains fluid and continues to move, and somevesicles that result from escaping gases develop at the top ofthe flow. Few open spaces develop in the center of the flowbecause it cools slowly. Thus, the flow center forms a dense,low-permeability zone between two more permeable zones.Thin flows cool more quickly than thick flows, and accordinglythe centers of thin flows commonly are broken and vesicularlike the tops and bottoms of the flows.
The Snake River Plain regional aquifer system in south-ern Idaho and southeastern Oregon (fig. 42) is an exampleof an aquifer system in basaltic rocks. The Snake River Plainis a large graben-like structure that is filled with basalt of Mi-ocene and younger age (fig. 43). The basalt consists of a largenumber of flows, the youngest of which was extruded about2,000 years ago. The maximum thickness of the basalt, as es-timated by using electrical resistivity surveys, is about 5,500feet. The basalt is bounded at the margins of the plain by si-licic volcanic and intrusive rocks that are downwarped towardthe plain.
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NOT TO SCALE
Chattanooga Shale
Warsaw Limestone and
Fort Payne Formation
St Louis Limestone
Ste Genevieve LimestoneGirkin Limestone
GreenRiver
Big Clifty SandstoneMember of GolcondaFormation
Sinkhole
SinkholeSinkhole
Swallow hole
Perched watertable
Well AWell B
Spring
Spring
NW SE
Mammoth Cave Plateau Pennyroyal Plain
Water table
37°
39° 83°85°
87°
89°K E N T U C K Y
Mammoth Cave
PlateauMammoth Cave Area
Pennyroyal
Plain
1953 1954 1955 1956 1957J DJ DJ DJ DJ D
0
10
20
422
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418
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412
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406
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PR
EC
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AT
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,IN
INC
HE
SW
AT
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VE
L, IN
FE
ET
BE
LOW
LA
ND
SU
RFA
CE
A
B
Well
Well
Flow top–vesicular,scoriaceousand broken;substantialpermeability
Flow center–dense, fewvesicles, mostfractures arevertical; mini-mal permeability
Flow bottom–vesicular andbroken; substan-tial permeability
Modified from Whitehead, 1992Base modified from U.S. Geological Surveydigital data, 1:2,000,000, 1972
Modified from Whitehead, 1992
■Thousand
Springs
W A S H I N G T O N
O R E G O N I D A H O
Snake
River
Snake
River
Co lumbiaRiver
Columbia
Riv
er
Pa
ci f
i cO
ce
an
120°
115°
48°
43°
●
●
●
●Seattle
Spokane
Olympia
Portland
Salem
Eugene
Boise
Pocatello●
★
★
★
YellowstoneNational Park
EXPLANATION
Direction of ground-water movement
EXPLANATION
Snake River Plain regional aquifer system
Figure 38. Large volumesof water move rapidly fromsinkholes and swallow holesthrough a well-developed net-work of solution cavities in theSt. Louis and Ste. GenevieveLimestones to discharge atsprings or to the Green River.The openings were formed bydissolution of the limestones aswater moved along beddingplanes and fractures.
Figure 39. Water levels inwells completed in sandstoneand carbonate-rock aquifersrespond differently to recharge.Changes in the water level inwell A, completed in sandstone,show that the sandstone isrecharged quickly but drainsslowly. In contrast, changes inthe water level in well B, opento underlying limestoneformations, show that rechargeto and discharge from thecarbonate-rock aquifer are rapiddue to large solution openingsin the limestone.
Figure 40. Pillow basalt forms when basaltic lava enters waterand cools quickly. Extensive interconnected pore spaces develop inthe flow as the ball-shaped pillows cool.
Figure 41. A typical basalt flow contains zones ofvarying permeability. Vesicular, broken zones at the top andbottom of the flow are highly permeable, whereas the densecenter of the flow has minimal permeability.
Figure 42. The Snake River Plain, which is located insouthern Idaho and southeastern Oregon, is underlainby basalt aquifers.
Sandstoneand carbonate-rock aquifers
Basalticand otherVolcanic–rockaquifers
Modified from Brown, 1966;and Quinlan and others, 1983
Modified from Brown, 1966
R.L. Whitehead 1980
0 5025 MILES
0 5025 KILOMETERS
SCALE 1:7,500,000
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