Lake Tecopa

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Coordinates: 35°52′30″N 116°15′00″W / 35.87500°N 116.25000°W / 35.87500; -116.25000[1]
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Reconstruction of Amargosa River lakes in the Pleistocene

35°52′30″N 116°15′00″W / 35.87500°N 116.25000°W / 35.87500; -116.25000[1] Lake Tecopa is a

tectonic basin close to the border with Nevada. Fed by the Amargosa River and some neighbouring washes, it eventually culminated to a surface area of 235 square kilometres (91 sq mi) around 186,000 years ago and left sediments. Afterwards, the Amargosa River cut a gorge out of the lake and into Death Valley with its Lake Manly, draining the lake. The present-day towns of Shoshone, California and Tecopa, California
lie within the basin of the former lake.

Hydrology

View from the Greenwater Valley over Tecopa CA to the Kingston Range. The terrain in the middle part of the image was formerly covered by Lake Tecopa

Lake Tecopa occupied the Tecopa Valley, a pear-shaped valley east of southern

marshes and deltas where Amargosa River or spring water entered the lake,[8] as well as freshwater ponds where springs and streams flowed into Lake Tecopa.[9]

At the time of the Bishop Tuff eruption, Lake Tecopa was about 100 metres (330 ft) deep.[10] The waters of the lake were salty and had a high pH,[11][10] inducing precipitation of calcite in the northern part of the lake where the Amargosa River flowed into it.[12] There is some indication that the centre of the lake was much more saline than its shores.[13] Salt lakes generally form when a lake has no outlet, so evaporation concentrates salts in the lake water until the lake contains saltwater.[14]

The Amargosa River at present-day Tecopa CA

The

washes that drain Chicago Valley and Greenwater Valley;[16][17] the total size of its catchment was about 8,300 square kilometres (3,200 sq mi) and most of its water originated in Paiute Mesa, Shoshone Mountains, Timber Mountains and Yucca Mountains.[18][5]

The catchment of the Amargosa River above Tecopa, California is presently about 8,000 square kilometres (3,100 sq mi). Later, after Lake Tecopa had disappeared, the river reached Death Valley and its Lake Manly,[10] dramatically increasing the supply of water to the latter.[19] Presently, the river is largely ephemeral except where it is fed by springs.[17]

Geography

The former lake basin is surrounded by various hills and mountain ranges, formed by rocks of

normal faults which separate grabens from horsts.[23] It was affected by extensive tectonic activity in the past and may be still active in the present.[24]

Presently, the towns of

oases in the area, including the locations of the three towns.[26]

Climate

Presently, the area of Lake Tecopa is a hot, dry desert with most precipitation occurring during summer. In Shoshone, California average temperatures are 19.5 °C (67.1 °F) and often exceed 45 °C (113 °F), with about 70 millimetres per year (2.8 in/year) of rainfall.[27][2] Under present-day climates, evaporation is too high and precipitation too low to allow the formation of lakes in the area.[9] 180,000 years before present, precipitation increased to 200–250 millimetres per year (7.9–9.8 in/year) and average temperatures decreased by 10.5 °C (50.9 °F), lifting the regional water tables.[27]

Sediments

See also: Tecopa Lake Beds

Various sediments were emplaced in the lake, including

adularia, clay, gravel and zeolites. Some of these formed when ash or sediments were progressively altered.[10][20] The sediments take the form of calcareous, sandy, silty material or mudstone.[12][20] The sediments have undergone increasing amounts of diagenesis the closer they are to the basin center. Among the minerals found at various sites are calcite, gaylussite, halite and sepiolite.[20]

After the lake was breached, these deposits were deeply eroded and exposed,

pumicite took place from the 1920s to the 1950s.[30]

Tufa deposits are found within the lake and partly embedded in its sediments; they were generated from carbonate precipitation within the lake, a process facilitated by the physical properties of the lake water.[31] Many of these tufa deposits occur where fault-controlled springs discharged water into the lake.[32]

Several tephra layers have been identified, including the 2.003 million years old Huckleberry Ridge Tuff, the 706,000 years old Bishop Tuff and the 602,000 years old Lava Creek Tuff[10][20] as well as the 2, 1.2-0.8 million years old Glass Mountain tuffs.[33] They form tuff layers which are very conspicuous in the lake sediments.[3]

Biology

A number of fossils were discovered in the sediments, including

muskrat.[36] Footprints have been observed at the edges of the lake basin.[20]

Centropyxis constricta, Lobatula lobatula and a few other, less widespread species. Foraminifera are mostly oceanic, and since Lake Tecopa was never connected to the ocean, they were most likely transported there by birds.[37]

History

Pleistocene lakes in the region. Note that Lake Tecopa's borders are incorrect

Lake Tecopa existed during the

magmatic activity may be occurring north of Shoshone.[18] From about 5 million years ago to about 186,000 years before present, the lake developed inside the basin.[17]

Extensive faulting of lake deposits makes it difficult to reconstruct its history.

oxygen isotope stages 8, 7 and 6.[44] Some doubts have been raised about this chronology, however.[45]

At some point after 579,000 years ago, a 8 square kilometres (3.1 sq mi) large

uplift in parts of the southern basin.[49]

About 200,000 - 150,000 years before present, the lake overflowed and disappeared.

river capture-like process or by overflow.[6] Subsidence in Death Valley may be ultimately responsible for the drainage change.[23] It is possible that Lake Tecopa briefly reformed later, due to a temporary blockage of its outflow,[51] and that at times the Amargosa River was blocked upstream from Lake Tecopa.[52]

The existence of the lake beds was described first by Levi F. Noble in 1926. In 1931, Eliot Blackwelder identified these lakebeds as the remnants of what he named Lake Tecopa.[17] The area of the former lake has been the subject of numerous studies comprising various fields of geology but also biology, and an important target for field studies and field trips.[53] Research in the paleoclimatic conditions of the region has received impetus from the Yucca Mountain nuclear waste repository, since the future climate of the region is important in establishing how secure the nuclear waste would be.[18][54]

References

  1. ^ a b Morrison 1999, p. 302.
  2. ^ a b Morrison 1999, p. 301.
  3. ^ a b c d Patterson 1987, p. 333.
  4. ^ a b Sheppard & Gude 1968, p. 1.
  5. ^ a b c d e Morrison 1999, p. 304.
  6. ^ a b Morrison 1999, p. 317.
  7. ^ Sheppard & Gude 1968, p. 4,5.
  8. ^ Larsen 2008, p. 619.
  9. ^ a b Gibert et al. 2011, p. 150.
  10. ^ a b c d e f g h i Nelson et al. 2001, p. 660.
  11. ^ Sheppard & Gude 1968, p. 33.
  12. ^ a b Sheppard & Gude 1968, p. 9.
  13. ^ Patterson 1987, p. 335.
  14. ^ Larsen 2008, p. 612.
  15. ^ a b Larsen 2008, p. 614.
  16. ^ a b Sheppard & Gude 1968, p. 4.
  17. ^ a b c d e f Morrison 1999, p. 303.
  18. ^ a b c d e Morrison & Mifflin 2000, p. 362.
  19. ^ Morrison 1999, p. 316,317.
  20. ^ a b c d e f g h Gibert et al. 2011, p. 149.
  21. ^ a b Nelson et al. 2001, p. 661.
  22. ^ a b Gibert et al. 2011, p. 148.
  23. ^ a b c Louie, John N.; Cetintas, Arif; Chekuri, Vijay; Corchuelo, William D.; Li, Li; Lei, Yutian; Mekala, Govardhan; Ozalaybey, Serdar; Raskulinecz, John. "Geophysical constraints on the cessation of extension and thickness of basin fill in Tecopa Valley, California". crack.seismo.unr.edu. The Nevada Seismological Laboratory. Retrieved 6 December 2017.
  24. ^ Morrison 1999, p. 330.
  25. ^ Reheis et al. 2019, p. 3.
  26. ^ Morrison & Mifflin 2000, p. 371.
  27. ^ a b Larsen 2008, p. 636.
  28. ^ Kodikara, McHenry & van der Meer 2023, p. 3.
  29. ^ Kodikara, McHenry & van der Meer 2023, p. 15.
  30. ^ Sheppard & Gude 1968, p. 2.
  31. ^ Nelson et al. 2001, p. 664,665.
  32. ^ Nelson et al. 2001, p. 669.
  33. ^ Reheis et al. 2019, p. 2.
  34. ^ Sheppard & Gude 1968, p. 6.
  35. doi:10.1080/08912963.2022.2103694
    .
  36. ^ Patterson 1987, p. 334.
  37. ^ Patterson 1987, p. 341.
  38. ^ a b Nelson et al. 2001, p. 659.
  39. ^ a b Morrison 1999, p. 311.
  40. ^ Reheis et al. 2019, p. 13.
  41. ^ Larsen 2008, p. 628.
  42. ^ Patterson 1987, p. 342.
  43. ^ Larsen 2008, p. 637.
  44. ^ Morrison & Mifflin 2000, p. 365,366.
  45. ISBN 9780813711997
    .
  46. ISSN 0091-7613
    .
  47. ^ Gibert et al. 2011, p. 157.
  48. ^ Morrison & Mifflin 2000, p. 368,369.
  49. ^ Reheis et al. 2019, p. 4.
  50. ^ Morrison 1999, p. 307.
  51. ^ Morrison 1999, p. 323.
  52. ^ Reheis et al. 2019, p. 26.
  53. ^ Reheis et al. 2019, p. 1.
  54. ^ Morrison 1999, p. 340.

Sources

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