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Theater-shaped channel heads are characterized by overhanging sidewalls that are relatively dry compared to the lower level rocks below the zone of seepage. The development of theater heads has been related to “ground-water flow direction, jointing and faulting, permeability contrasts, formation slope and dip angles, and formation cohesion”. The morphology of channels and valleys created by sapping are highly dependent on regional scale geology, and can be hard to distinguish from features created through alternative processes. Chemical precipitates can be used as indicators of groundwater water discharge implying that a valley or channel may have been formed as a result of sapping. These sorts of clues are important in areas where water is not currently being discharged.
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52:. As the surge of water and sand brought to land by a wave retreats seaward, the film of water becomes thinner until it forms rhomboid shaped patterns in the sand. Small fans form at the apex of the rhombic features, which are eventually fed by the remaining backflow of water traveling downslope. Channels begin to form headward in the form of millimeter wide rills along the sides of the fans; the creation of these small channel networks culminates when the last of the backwash dissipates.
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Characteristic landforms caused by groundwater sapping are “theater-shaped” channel heads and “U-shaped” valleys, which have a consistent width and steep valley walls. Weakened basal rocks are unable to support more resistant upper layers, causing valley head and sidewalls to collapse inwards.
178:. It is thought that sapping may have been more common in this area in the past when there was a higher water table. A shift in the climate and associated precipitation or the incision of the Colorado River are two factors that may have caused a change in the water table level.
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erosion process that results in the headward migration of channels in response to near constant fluid discharge at a fixed point. The consistent flow of water displaces fine sediments which physically and chemically weathers rocks. Valleys that appear to have been created by
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Short, stream-like, deep channels have been observed on Mars. Very similar to valleys created by groundwater sapping here on Earth, the discovery of the
Martian valleys has prompted numerous studies that aim to better understand the process of sapping.
473:
Julie E. Laity and
Michael C. Malin, "Sapping processes and the development of theater-headed valley networks on the Colorado Plateau," Geological Society of America Bulletin: Vol. 96, No. 2 (1985), pp. 203–217
44:, and many other places. However, it is difficult to characterize a landform as being formed exclusively by groundwater sapping due to phenomena such as pluvial runoff, plunge-pool undercutting, changes in
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associated with high water tables underlain by an impermeable layer. Limited in its ability to travel vertically, water is forced to travel laterally where it eventually seeps out of the ground.
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that become wider with distance from their source. Groundwater sapping has been suggested as the cause for erosion of the valley and channel networks on
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level, and inconsistent groundwater flow. An example of drainage ways created purely by the outflow of subsurface fluids can be seen on the foreshores of
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Kochel, R.C.; Piper, J.F. (1986). "Morphology of Large
Valleys on Hawaii: Evidence for Groundwater Sapping and Comparisons with Martian Valleys".
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83:, although studies show that groundwater alone can not excavate and transport the material required to create these canyons.
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Higgins, C.G. (1984). "Piping and
Sapping: Development of Landforms by Groundwater Outflow". In LaFleur, R.G. (ed.).
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Nash, D.J. (1996). "Groundwater
Sapping and Valley Development in the Hackness Hills, North Yorkshire, England".
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481:"Comparing morphologies of drainage basins on Mars and Earth using integral-geometry and neural maps"
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291:"Formation of Box Canyon, Idaho, by Megaflood: Implications for Seepage Erosion on Earth and Mars"
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Gulick, V.C. (2001). "Origin of the Valley
Networks on Mars: a Hydrological Perspective".
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Lamb, M. P.; Dietrich, W. E.; Aciego, S. M.; Depaolo, D. J.; Manga, M. (2008).
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Alan D. Howard, "Introduction: Groundwater
Sapping on Mars and Earth" in
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522:"Quantifying Groundwater-sapping Landforms with a Hyposemetric Technique"
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Scientists believe that groundwater sapping created these gullies in
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heads typical of valley features shaped by groundwater sapping. The
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can be found in valleys created by groundwater sapping as well.
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Ground-water
Sapping and the Generation of Natural Ampitheaters
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This is one of the processes involved in the formation of
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of fairly uniform width with box-like, "theater-shaped"
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sapping occur throughout the world in areas such as
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143:The two canyons at center-left in this photo from
240:. Boston, MA: Allen and Unwin. pp. 18–58.
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466:Sapping Features of the Colorado Plateau
75:pattern of V-shaped valleys produced by
479:Stepinski, T.F.; Coradetti, S. (2004).
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106:Sapping typically occurs in permeable
256:Earth Surface Processes and Landforms
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526:Journal of Geophysical Research
378:Journal of Geophysical Research
238:Groundwater as a Geologic Agent
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433:10.1016/s0169-555x(00)00086-6
485:Geophysical Research Letters
262:(9) (9 ed.): 781–795.
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145:Canyonlands National Park
102:Geomorphology and geology
356:"University of Colorado"
126:Characteristic landforms
398:10.1029/jb091ib13p0e175
318:10.1126/science.1156630
213:Valley networks (Mars)
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208:Groundwater discharge
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546:10.1029/1999je001096
505:10.1029/2004GL020359
354:Rosenberry, Donald.
538:2000JGR...105.1685L
497:2004GeoRL..3115604S
425:2001Geomo..37..241G
390:1986JGR....91E.175K
310:2008Sci...320.1067L
304:(5879): 1067–1070.
268:1996ESPL...21..781N
17:Groundwater sapping
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135:Notable landmarks
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532:(1): 1685–1694.
520:Lou, W. (2000).
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474:(Abstract).
157:Green River
96:NASA image.
46:water table
42:New Zealand
26:groundwater
557:Categories
219:References
116:siltstones
112:Limestones
108:sandstones
59:, such as
21:geomorphic
151:have the
94:on Mars.
73:dendritic
69:headwalls
573:Aquifers
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334:30609556
326:18497296
197:See also
34:Colorado
534:Bibcode
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386:Bibcode
306:Bibcode
298:Science
264:Bibcode
57:gullies
50:beaches
38:Hawai’i
30:England
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120:shales
118:, and
61:lavaka
509:S2CID
330:S2CID
294:(PDF)
19:is a
322:PMID
188:Mars
182:Mars
149:Utah
81:Mars
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