Lake Manly
Lake Manly was a pluvial lake in Death Valley, California. It forms occasionally in Badwater Basin after heavy rainfall, but at its maximum extent during the so-called "Blackwelder stand," ending approximately 120,000 years before present, the lake covered much of Death Valley with a surface area of. Water levels varied through its history, and the chronology is further complicated by active tectonic processes that have modified the elevations of the various shorelines of Lake Manly; during the Blackwelder stage they reached above sea level. The lake received water mainly from the Amargosa River and at various points from the Mojave River and Owens River. The lake and its substantial catchment favored the spread of a number of aquatic species, including some lizards, pupfish and springsnails. The lake probably supported a substantial ecosystem, and a number of diatoms developed there.
In Death Valley, lakes existed during different times in the geological past. After some poorly defined lake stages during the Miocene, Pliocene and early Pleistocene, the first large lake stage occurred about 185,000–128,000 years ago during the Tahoe glacial stage and formed the Blackwelder shorelines. This lake was the largest known extent of Lake Manly; theories that the lake merged with Lake Mojave farther south or even overflowed into the Colorado River close to Ludlow and across several other basins are, however, questionable. After the drying of this lake a later lake stage occurred 35,000–10,000 years ago during the Tioga/Wisconsin glaciation; this lake was smaller than the Blackwelder lake. During the Holocene, the lake disappeared; today only ephemeral lakes occur in Death Valley during strong floods.
This lake is one among many major lakes that formed in the Great Basin, the best researched of which are Lake Lahontan and Lake Bonneville. Decreasing temperatures and thus decreased evaporation rates as well as increased precipitation rates during the ice ages were responsible for the formation of these lake systems. Lake Manly collected the overflow from a number of lakes including Lake Tecopa, Mono Lake, Owens Lake, Searles Lake, Lake Panamint, Lake Mojave, Lake Dumont and Lake Manix. Not all of them existed or drained into Lake Manly simultaneously.
Discovery and naming
The existence of large ancient lakes in the Great Basin of the United States was already proposed by the end of the 19th century, when the existence of Lake Lahontan and Lake Bonneville was first described. The possibility of a former lake in Death Valley was also considered during that time, though at first it was not universally accepted as a large lake. The first evidence for it was described in 1924 by geologist Levi F. Noble. Earlier in 1890 another geologist, Grove Karl Gilbert, already assumed a lake existed in Death Valley, although his lake was considerably larger than actual Lake Manly.Evidence for the lake's existence includes wavecut terraces observed by geologists in 1925, pebbles and tufa, layers of clay and salt on its former lake bed, and calcium carbonate deposits that were probably formed by algae in the lake. These clues are dispersed across Death Valley, especially within the more researched areas of Beatty Junction and Desolation Canyon.
While the deposits were once attributed to a single lake stand, later evidence was found of various lake cycles going back to the Pliocene. The history of Lake Manly is not as well understood as that of Lake Lahontan and Lake Bonneville, the two largest pluvial lakes recorded in the Great Basin. More recently, renewed scientific interest has stemmed from the fact that Lake Manly formerly drained the area of Yucca Mountain, a proposed nuclear waste repository.
The lake was named in honor of William Lewis Manly, who rescued his traveling party stranded in Death Valley in 1849. The name "Lake Rogers" for a potential northern lake in Death Valley was derived from a compatriot of Manly, John Rogers. The name "Lake Manly" was coined in 1932, and is sometimes spelled as "Manley", which is a misspelling. Other names for the lakes in Death Valley are "Death Valley Pleistocene lakes" and "Death Valley Lake", a name first used in a publication of 1902.
The name is used for the lakes that occupied Death Valley in the past, but occasionally the name "Lake Manly" is used only for the most recent, the middle Pleistocene lake stage or general late Pleistocene lake stages.
Geography
Lake Manly formed in Death Valley, a tectonic depression framed by the Cottonwood Mountains and Panamint Range to the west, Owlshead Mountains to the south and Black Mountains, Funeral Mountains and Grapevine Mountains to the east. Death Valley is about long and wide and consists of three basins: Badwater Basin which reaches a depth of beneath sea level, Cottonball Basin and Middle Basin. The Badwater Basin is the deepest point in North America. Death Valley began forming about 14 million years ago, and by the Pliocene it was well developed. The valley remains deep due to vertical faulting, which occurs faster there than anywhere else in the US. Various types of rocks form the surface areas of Death Valley, some going back as far as the Precambrian.The Death Valley is tectonically active, with faults including the Black Mountains fault, Furnace Creek Fault, Grandview Fault, Northern Death Valley Fault, Southern Death Valley fault and Towne Pass Fault. Thus, shorelines from the same lake stands are often not at the same elevation in various parts of the basin. Faulting has caused a progressive drop in elevation of the floor of Death Valley, keeping pace with sedimentation, though the exact rates are not known. This deformation causes the southwestern shores of Lake Manly to sag with respect to the northeastern ones, and together with sedimentation renders estimating the depth of Lake Manly unreliable. This is compounded by the fact that many lake deposits are located close to the active faults of the Death Valley fault zone. Over the last 60,000–70,000 years, the Northern Death Valley fault zone has slipped by about. Lack of earthquakes and dates makes it difficult to estimate the activity of these faults, though an earthquake occurred in 1908, and Death Valley is actively subsiding. Volcanism has also affected Death Valley, including Ubehebe Crater in the valley and the distant Mono-Inyo Craters, all within the last 2,000 years.
The lake
Lake Manly was a long, narrow lake with a southern sub-basin named "Confidence Flats". It was about deep at highstand, and about above sea level. The lake reached a width of and length of. The shores of the lake were long. The most prominent shoreline at about elevation is known as "Blackwelder shoreline"; even higher shorelines have been identified at Shoreline Butte. At this stand, the lake had a surface area of about using present-day topography; at that point the volume would have been about. The absolute highest surface area Lake Manly could have had was or. Some landforms indicative of lacustrine deposition have been found at altitudes of above sea level around Death Valley but they could also be the consequences of non-lacustrine processes.Southern California and southern Nevada contain deserts with valleys similar to Death Valley that are also not formed by rivers. Many of them held water in the past; some lakes such as Great Salt Lake, Mono Lake, Pyramid Lake and Walker Lake still exist. These ancient lakes were ultimately generated by Basin and Range province tectonic phenomena which caused runoff to collect in closed basins. Various weather changes associated with the last glacial maximum favored their infilling, including southward shifts of storm tracks accompanying analogous shifts of the jet stream, which were probably forced by the Laurentide Ice Sheet. Currently a salt pan fills Death Valley, with an average surface altitude of.
One island existed close to Beatty Junction, with two more at Shoreline Butte in the southernmost point of the lake; the northern foot of the Avawatz Mountains may have formed a peninsula on the southern shore. No river deltas or other embankments have been found at Lake Manly's shorelines; their formation was likely hampered by unstable water levels. Only vague remnants of a delta are found where the Amargosa River probably entered Lake Manly, and the alluvial fan of Warm Springs Canyon is cut by shorelines of Lake Manly. Chevrons and pisolites have been found in lake sediments. A number of alluvial fans decorate the former shores of Lake Manly.
Shorelines
Landforms associated with Lake Manly have been identified at a number of points in Death Valley. At Beatty Junction, winds on the lake formed several spits and barrier bars. Shorelines at Desolation Canyon also included spits and a tombolo. Just south of Desolation Canyon, the so-called Manly Terraces are a group of terraces. At least 12 different terraces have been found at Shoreline Butte.A number of bars and spits formed on the shores of Lake Manly and are preserved to this day. Some rocks in shoreline deposits left by the lake display evidence of honeycomb weathering. The southern shore of Lake Manly was formed by alluvial fans that had coalesced at the foot of the Avawatz Mountains; these fans are still growing and displacing the Amargosa River eastwards. Some sand and gravel deposits at Salt Spring Hills with elevations of about may have been formed by either Lake Manly or another paleolake south of Death Valley, Lake Dumont.
The shores of Lake Manly were influenced by wave action. These waves probably came predominantly from the north-northwest, causing near shore material to be transported to the south. This also explains why most of the shore features are found on the eastern shores of the lake as these were the most exposed to wave action. It is not always clear whether a strandline is actually a strand line or a surface expression of fault activity; some supposed lower strandlines at Mormon Point were later reinterpreted as fault scarps.