Lake Alamosa
Lake Alamosa | |
---|---|
Location | San Luis Valley, Colorado |
Coordinates | 37°12′N 105°25′W / 37.200°N 105.417°W |
Type | former lake |
Basin countries | United States of America |
Lake Alamosa is a
The lake eventually overflowed into the Rio Grande river system during the middle Pleistocene. The overflow cut down a valley that eventually drained the lake, leaving only the San Luis Closed Basin as a remnant. The Alamosa Formation is a rock formation left by the lake. Groundwater resources are contained trapped between sediments left by the former lake.
Description
The lake was in southern Colorado, at high altitude, covering most of the San Luis Valley[1]/San Luis Basin north of the San Luis Hills.[2] It reached an elevation of 2,335 meters (7,661 ft) at highstand.[3] Westwards, Lake Alamosa spread to the San Juan Mountains close to Monte Vista to the west. Northwards, it almost reached the present-day location of Saguache.[2] It was about 105 kilometers (65 mi) long in north-south direction and reached a maximum width of 48 kilometers (30 mi),[4] making it one of North America's largest high elevation lakes, comparable only to the historic Lake Texcoco in Mexico.[1] The surface area may have exceeded 4,000 square kilometers (1,500 sq mi) at highstand.[5] It is likely that some water seeped out of the lake before its final overflow[6] as groundwater.[7]
Because of the old age of Lake Alamosa, shorelines and shoreline features are often buried or eroded; in many places former shorelines are only highlighted by changes in vegetation patterns or slope angle.
Climate
During the glacial times of Lake Alamosa's existence, the basin was colder than today and possibly also drier. The lake was nourished by
Geologic history
The San Luis Basin is the largest
Lake Alamosa existed for about 3 million years,
Many lakes in western North America are cyclical, becoming deep and large during
Overflow
It overflowed about 440,000 years ago,
Lake Alamosa overflowed through the
Water levels dropped quickly after the overflow began, preventing the formation of the repeated shorelines that are common at shrinking pluvial lakes[31] where the decline in water levels is paced by evaporation.[33] The decline probably was not as quick as during the Bonneville flood of Lake Bonneville, another example of a lake overflow event in North America, as the rocks at Lake Alamosa were more solid and there is no clear indication of a catastrophic overflow flood.[32] Later research has indicated that the downcutting of the outlet may have continued for several hundred thousand years after the initial breach,[34] and was accompanied by an integration of the Rio Grande all the way to the Gulf of Mexico.[34] That the lake drained after groundwater sapping has also been postulated but is less likely.[35]
After the overflow
After the drainage of the lake the lakefloor was eroded by streams, which redeposited its sediments, and soils formed.[3] The lake would have been replaced by dry lakes and anastomosing stream networks.[36] Creeks cut into the lake floor, forming valleys that later filled with alluvium.[33]
The Alamosa Formation, a geological formation, fills the basin of Lake Alamosa;[13] it represents the deep water deposits of Lake Alamosa.[37] Impermeable deposits of the lake such as the "blue clay"[17] generate groundwater accumulations that are exploited for irrigation purposes.[38] The Verdos Alluvium of the Denver Basin may correlate to certain deposits on the shores of Lake Alamosa.[39]
While it was formerly thought that the
Research history
Decades before the region was settled and earlier than other geologic expeditions such as those of John Wesley Powell,[30] in 1811-1812 Jacob Fowler recorded the following:[29]
I Have no doubt but the River from the Head of those Rocks up for about one Hundred miles Has once been a lake of about from forty to fifty miles Wide and about two Hundred feet deep—and that the running and dashing of the Watter Has Woren a Way the Rocks So as to form the present Chanel.
Jacob Fowler
The lake is named after the Alamosa Formation, which in turn received its name from Siebenthal 1910[1] who in that year postulated the existence of a former lake in the Alamosa Basin.[8] In the same year proof of the existence of the lake was found in well logs.[1]
Later, the geologist
References
- ^ a b c d e f g Machette, Coates & Johnson 2007, p. 157.
- ^ a b c Machette, Coates & Johnson 2007, p. 64.
- ^ a b c Machette, Coates & Johnson 2007, p. 58.
- ^ a b c Machette, Coates & Johnson 2007, p. 74.
- ^ a b Blair & Bracksieck 2011, p. 66.
- ^ a b Repasch et al. 2017, p. 121.
- ^ Repasch et al. 2017, p. 141.
- ^ a b c Machette, Coates & Johnson 2007, p. 158.
- ^ Madole et al. 2013, p. 443.
- ^ Yuan, Koran & Valdez 2013, p. 147.
- ^ Mayo, Davey & Christiansen 2006, p. 406.
- ^ a b Machette, Coates & Johnson 2007, p. 78.
- ^ a b c d e Machette, Coates & Johnson 2007, p. 53.
- ^ Machette, Coates & Johnson 2007, p. 63.
- ^ Machette, Coates & Johnson 2007, p. 160.
- ^ a b c d e Machette, Coates & Johnson 2007, p. 164.
- ^ a b c d Machette et al. 2013, p. 107.
- ^ a b c Machette, Coates & Johnson 2007, p. 73.
- ^ Repasch et al. 2017, p. 137.
- ^ Ruleman et al. 2019, p. 6.
- ^ Repasch et al. 2017, p. 136.
- ^ Ruleman et al. 2019, p. 18.
- ^ Machette, Coates & Johnson 2007, p. 104.
- ^ Machette, Coates & Johnson 2007, p. 88.
- ^ Machette, Coates & Johnson 2007, p. 86.
- ^ Madole et al. 2013, p. 442.
- ^ Machette et al. 2013, p. 115.
- ^ Repasch et al. 2017, p. 122.
- ^ a b Machette, Coates & Johnson 2007, p. 71.
- ^ a b c Machette, Coates & Johnson 2007, p. 72.
- ^ a b Machette, Coates & Johnson 2007, p. 75.
- ^ a b Machette, Coates & Johnson 2007, p. 76.
- ^ a b Machette, Coates & Johnson 2007, p. 60.
- ^ a b Ruleman et al. 2019, p. 27.
- ^ Machette, Coates & Johnson 2007, p. 166.
- ^ Ruleman et al. 2019, p. 21.
- ^ Machette, Coates & Johnson 2007, p. 77.
- ^ Machette, Coates & Johnson 2007, p. 161.
- ^ Ruleman et al. 2011, p. 31.
- ^ Madole et al. 2013, p. 441.
- ^ Madole et al. 2013, p. 444.
- ^ Machette, Coates & Johnson 2007, p. 159.
- ^ Machette, Coates & Johnson 2007, p. 57.
Sources
- Blair, Rob; Bracksieck, George (2011-09-01). The Eastern San Juan Mountains: Their Ecology, Geology, and Human History. University Press of Colorado. ISBN 978-1-60732-085-2.
- Machette, Michael N.; Thompson, Ren A.; Marchetti, David W.; Smith, Roger S.U. (2013), "Evolution of ancient Lake Alamosa and integration of the Rio Grande during the Pliocene and Pleistocene", New Perspectives on Rio Grande Rift Basins: From Tectonics to Groundwater, Geological Society of America, ISBN 978-0-8137-2494-2, retrieved 2020-07-05
- Machette, M.N.; Coates, M-M.; Johnson, M.L. (2007). 2007 Rocky Mountain Section Friends of the Pleistocene Field Trip—Quaternary geology of the San Luis Basin of Colorado and New Mexico, September 7–9, 2007. U.S. Geological Survey Open-File Report 2007–1193 (Report).
- Madole, Richard F.; Mahan, Shannon A.; Romig, Joe H.; Havens, Jeremy C. (1 November 2013). "Constraints on the age of the Great Sand Dunes, Colorado, from subsurface stratigraphy and OSL dates". Quaternary Research. 80 (3): 435–446. S2CID 129821857.
- Mayo, Alan L.; Davey, Allen; Christiansen, David (10 November 2006). "Groundwater flow patterns in the San Luis Valley, Colorado, USA revisited: an evaluation of solute and isotopic data". Hydrogeology Journal. 15 (2): 383–408. S2CID 129460791.
- Repasch, Marisa; Karlstrom, Karl; Heizler, Matt; Pecha, Mark (1 May 2017). "Birth and evolution of the Rio Grande fluvial system in the past 8Ma: Progressive downward integration and the influence of tectonics, volcanism, and climate". Earth-Science Reviews. 168: 113–164. ISSN 0012-8252.
- Ruleman, C.A.; Bohannon, R.G.; Bryant, Bruce; Premo, W.R. (2011). Geologic map of the Bailey 30' x 60' quadrangle, North-Central Colorado: U.S. Geological Survey Scientific Investigations Map 3156, scale 1:100,000 (Report).
- Ruleman, Chester A.; Hudson, Adam M.; Thompson, Ren A.; Miggins, Daniel P.; Paces, James B.; Goehring, Brent M. (1 November 2019). "Middle Pleistocene formation of the Rio Grande Gorge, San Luis Valley, south-central Colorado and north-central New Mexico, USA: Process, timing, and downstream implications". Quaternary Science Reviews. 223: 105846. S2CID 204253674.
- Yuan, Fasong; Koran, Max R.; Valdez, Andrew (15 December 2013). "Late Glacial and Holocene record of climatic change in the southern Rocky Mountains from sediments in San Luis Lake, Colorado, USA". Palaeogeography, Palaeoclimatology, Palaeoecology. 392: 146–160. ISSN 0031-0182.
External links
- Beeton, Jared Maxwell; Saenz, Charles Nicholas; Waddell, Benjamin James (2020). The geology, ecology, and human history of the San Luis Valley. Louisville. ISBN 978-1-64642-040-7.)
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