Discovery and naming Edit

Geography Edit

Hydrology Edit

Climate Edit

The mean annual temperature of Death Valley is about 26 °C (79 °F), due in part to its relatively low elevation; July temperatures exceed 38 °C (100 °F) on average. Based on plant data, summer temperatures at Lake Manly during the Pleistocene were about 6–8 °C (11–14 °F) lower than present day; Yucca whipplei was found at altitudes too cold for its development, suggesting that middle altitudes winters were milder 12,000–10,000 years ago. Winter water temperatures may have dropped below 10 °C (50 °F) however, occasionally falling below 0 °C (32 °F) with a maxima of 19–30 °C (66–86 °F) during the latest lake stage. The "Blackwelder" stage had higher maximum temperatures. Maximum temperatures were depressed by 4–15 °C (7–27 °F) during summers in the last highstand; Blackwelder highstand temperatures reached 25–32 °C (77–90 °F), however. Death Valley has a dry climate, owing to the rain shadow formed by the Panamint Range and the Sierra Nevada, which is enhanced by the relative depth of the valley. Thus less than 50 millimetres (2.0 in) precipitation fall every year, and large year-to-year variations are observed. Much of this rainfall is transported by winter storms, although summer thunderstorms and tropical storms also contribute. The depression of the forest line in Death Valley suggests that during the Pleistocene, rainfall was three or four times what it is today. Based on hydrological modelling, a temperature drop of about 10 °C (18 °F) and 2.5 times today's precipitation would be needed to recreate the last highstand of Lake Manly. Lake Manly was probably windier than present-day Death Valley, as present day winds would not be strong enough to push some of the rocks that were moved along Lake Manly's shores; wind speeds of over 31 metres per second (100 ft/s) would be needed. Later research reduced this requirement to about 14–27 metres per second (46–89 ft/s), which is consistent with estimated present day wind speeds in Death Valley. The topography of the valley would have generated northerly winds over Lake Manly, but strong southwesterly winds also contributed to the formation of beach deposits. Wave heights have been estimated at about 76–94 centimetres (2 ft 6 in–3 ft 1 in) with heights of about 1.35–2.22 metres (4 ft 5 in–7 ft 3 in) needed to transport beach material, enough to form backwash and swash. Wave activity was most pronounced in the southern and northern parts of Lake Manly.

Biology Edit

Chronology Edit

Lake Manly existed during the late Pleistocene, and was at first considered to be an early Wisconsin glaciation (Tahoe stage) phenomenon. Originally, it was believed that Lake Manly did not exist during the Tioga glaciation, and it was assumed that Lake Manly existed in only one stage. Later evidence, such as drilling core data, indicates two distinct lake stages, one 185,000–128,000 years ago and another 35,000–10,000 years ago. This corresponds to oxygen isotope stage 6 and 2 respectively. Between 120,000 and 60,000 years ago there was no lake in Death Valley, and separate saline lakes existed between 60,000 and 35,000 years ago. Lake levels in Lake Manly appear to track the size of the Laurentide ice sheet but only very roughly so. Further, last glacial maximum highstands of Lake Manly appear to precede highstands of Lake Lahontan and Lake Bonneville, probably due to a northward shift of the jet stream. Earliest highstands Edit According to sedimentation patterns, a southeastward flowing river occupied northern Death Valley during the late Miocene, and was gone by 3.35 million years ago. This river system started in the Cottonwood Mountains – possibly as far as Last Chance Range and Owens Valley – and passed through northern Death Valley into the Amargosa Valley, possibly into the Colorado River. A Pliocene stage is documented in southern Death Valley,[27] and a lake in the Furnace Creek basin of northern Death Valley reached a highstand 3.35 million years ago; a number of tephra layers provide controls on the ages of this lake. Thus, a very early lake existed in northern Death Valley between 3.5 and 1.7 million years ago, or between 3.4 and <3 million years ago, probably coinciding with the beginning development of a glacial climate in North America at that time. Such a lake was connected with the Owens Valley because Coso volcanic field tuffs have been found in Death Valley. The basins occupied by early lakes were probably not the same as those of Lake Manly; tectonic deformation has lifted the Nova basin above the current floor of Death Valley. This lake was most likely of limited extent. The 1.7–1.9-million-year-old Glass Mountain tuffs formed deposits in such early lakes. In the early and middle Pleistocene, the Amargosa River and Mojave River ended in terminal lakes before reaching Death Valley, and it is not clear that the Owens River could overflow from Panamint Valley into Death Valley. Tephra interbedded with lake deposits indicates that a pre-Lake Manly existed between 1.2–0.8 million and 665,000 years before present. Simultaneous highstands in other Great Basin lakes such as Lake Bonneville may be correlated with this lake stage, which occurred during marine isotope stage 16. It is not clear whether this was one lake or several disconnected lakes.[175] Other old lake stands may have occurred 510,000 years ago and 216,000–194,000 years before present; shorelines from the latter stand are presently at altitudes of 73–96 metres (240–315 ft). The existence of Lake Manly 1,000,000–600,000 years ago is possible but questionable; yet older lake formations have been variously dated between 3.7 and 0.77 million years ago. These formations are known as "Lake Manly phase 1" or "Lake Zabriskie". Blackwelder highstand Edit The highest shoreline at elevations of 90–100 metres (300–330 ft) has been named Blackwelder stand, after a researcher who first examined the fossil shorelines. It appears to belong to the first (Illinoian) stage of the lake, but was originally thought to belong to the second (Wisconsinian) stage, during oxygen isotope stage 6. Additional shorelines associated with this highstand are found at elevations of 47–90 metres (154–295 ft). Uranium-thorium dating has linked this shoreline to the older highstand, about 186,000–120,000 years before present; an alternative proposal linking the Blackwelder stand with a wet period in Lake Searles 1.3–1 million years ago conflicts with other dates. The uranium-thorium dates and others of the Blackwelder stand are not beyond all doubts, however. A brief dry period may have occurred 148,000 years ago, possibly caused by a temporary damming of the Amargosa River.[180] Ostracod data indicates two separate highstands 154,500–149,000 and 122,000–120,000 years ago. Depending on the rate of tectonic sinking, the lake at the early stage was 175 metres (574 ft) and up to 335 metres (1,099 ft) deep. The Sperry terrace in Amargosa Canyon appears to be of the same general age as the Blackwelder highstand. During this time the Amargosa River and Owens River reached Lake Manly. Ostracod fossils from this lake stage suggest that the lake's conditions varied during this timespan. This shoreline is found at Mormon Point, Shoreline Butte and elsewhere in the northern Death Valley but not in the south; one theory states that shorelines at elevations of 180 metres (590 ft) (Salt Spring and Saddle Springs) and 340 metres (1,120 ft) (Mesquite Spring at Soda Lake) are Blackwelder shorelines that were offset by tectonic deformation at a geologically reasonable rate of 2 millimetres per year (0.079 in/year). Such would imply that Soda Lake and Silver Lake during the Blackwelder stand were connected with Lake Manly; this theory is known as "mega Lake Manly". Such an expansion would have occurred whenever the lake levels rose above 178 metres (584 ft) above sea level and thus could flow south across Salt Spring Hills; the enlargement of the lake surface that resulted would have increased evaporation and stabilized lake levels. There is no clear cut evidence that these shorelines are of the same age as the Blackwelder shoreline, although they are of similar appearance. The spread of pupfish between the Mojave River and Death Valley drainages would also be more likely with such a lake configuration. There is no indication that Soda Lake playa had a lake during oxygen isotope stage 6, although water currents in a previous lake may have transported sands that are usually only found in ephemeral lakes through a deeper lake. Further, based on dating, shorelines at Salt Spring appear to belong to the later lake stage, and the tectonic deformation required to link the two southern shorelines to the Blackwelder has been deemed implausible, and has not been supported by analysis of the shorelines themselves. A final explanation assumes that during that stage, Lake Manly did not extend into southern Death Valley.[27] The Blackwelder highstand was probably not stabilized by overflow seeing as the only spillway close to Ludlow is about 595 metres (1,952 ft) high above sea level – considerably higher than the Blackwelder highstand could plausibly be – and the highest shorelines at Shoreline Butte and Lake Mojave are considerably lower. Additionally, the development of stable shorelines does not by default require an overflow, as demonstrated by the Dead Sea and its precursor Lake Lisan. Later lake stages Edit By 130,000–120,000 years ago, Lake Manly had retreated from the Blackwelder highstand.[189] A further lake stage may have occurred during oxygen isotope stage 4, but evidence is equivocal. Ostracod fossils dated between 129,000 and 123,000 years ago indicate that Death Valley was wetter than today and supported several hydrological environments. Between 54,000 and 50,000 years ago various shallow phases of Lake Manly occurred. The later lake stage which occurred during the Wisconsin glaciation/Weichselian glaciation was not as large as the Blackwelder lake stage; at first it was suggested that only small lakes occupied Death Valley during that time. The later lake was shallower, with tufas dated at 25,000 and 18,000 years before present having formed at elevations of −22 to −30 metres (−72 to −98 ft). That lake was probably shallow, with estimated depths of 64–78 metres (210–256 ft). Later research indicated that late Lake Manly was even shallower, probably because regional climate conditions favorable to its growth were rarer during the later lake stage than at Blackwelder times, and might have even been split into two separate waterbodies. Further, it may have been dominated more by groundwater discharge. In general, the chronology of this recent lake stage is not very clear. The last glacial maximum lake had a surface area of about 1,600 square kilometres (620 sq mi). This lake stage had highstands approximately 26,000, 18,000 and 12,000 years before present, which have been named "DVLP-1" ("Death Valley Late Pleistocene lake high-stand"), "DVLP-2" and "DVLP-3" respectively. Some radiocarbon dates have been obtained on this lake, including 12,980 ± 700 and 11,900 ± 200. The recession commenced before 12,970 ± 185 years ago.[189] Present day Edit A reformed lake in 2005 By 12,000 years before present, Lake Manly had shrunk to the Badwater basin and was probably only 2 metres (6 ft 7 in) deep. This drying event separated various Cyprinodon populations from each other, triggering the evolution of individual species with restricted distribution. Based on the state of preservation of shoreline deposits (e.g., at Hanaupah Fan), the retreat of the lake was probably much faster than its growth. The lake had vanished by 10,000 years ago, although some evidence for a Holocene lake has been found. A minor lacustrine period occurred between 5,000 and 2,000 years ago; this lake was larger than Lake Mead and probably existed for less than 100 years. Its shorelines have been found at elevations of −79 to −73 metres (−260 to −240 ft). Since then, only a pond in Badwater basin remains, and the valley is hot and dry.[198] The rest of the valley floor is filled with mudflats and salt pans. Salt Creek and some springs are the only freshwater present. Floods of the Mojave River are lost before reaching Death Valley. Current evaporation rates and climate conditions do not allow the existence of perennial lakes in Death Valley. The bulk of present-day water in Death Valley is supplied by groundwater discharge. The Amargosa River is mostly underground, but occasionally it can flood and reach Death Valley. Parts of Death Valley are sometimes flooded during wet weather, causing parts of Lake Manly to reform. Legend has it that such happens only every hundred years. Severe flooding in March 2005 resulted in parts of Death Valley becoming submerged.[205] This precipitation event broke records dating back to 1911 and was followed by a major desert bloom.[198] Such lake refillings are usually associated with El Niño events.