18.4: Desert Landforms
Desert Landforms
In deserts like the Mojave and Great Basin of California, streams drain the mountains through canyons that emerge into adjacent valleys. As the stream emerges from these narrow canyons, the sediment they carry spreads out and is deposited due to the lack of confinement, low slope angle, and slower velocities. The stream channel begins to fill with this conglomeratic material, and the stream must adjust and deflects around the fill. This process will continue to occur, causing the stream to be deflected back and forth, developing a braided system and constructing a fan shaped feature called an alluvial fan Links to an external site.. Alluvial fans continue to grow and may eventually coalesce with neighboring fans to form an apron of alluvium along the mountain front called a bajada Links to an external site.. Eventually mountains become buried in their own erosional debris and are referred to as inselbergs Links to an external site. or “island mountains”.
Figure 18.10: Alluvial fan in Death Valley, California (top of photo), seen from source area of Black Mountains at Dante's View. (Public Domain; Mark A. Wilson/Wilson44691 Links to an external site.)
Where the desert valley is an enclosed basin, streams entering it do not drain out but the water is removed by evaporation. This forms a flat dry lake bed called a playa Links to an external site.. The playa lake that fills this flat area may cover a large area and be only a few inches deep, and that only after a heavy thunderstorm. Playa lakes and desert streams that fill and flow only after rainstorms are frequently intermittent or ephemeral Links to an external site..
⚒️Can You Dig It?
The famous Racetrack Playa Links to an external site. of Death Valley National Park perplexed scientists for years, as they attempted to explain the independent movement of cobbles and large boulders along flat surfaces (Figure 18.11). In 2014, several experimental and observational studies confirmed that thin layers of ice allow the stones to slip along the ground, with high winds providing propulsive energy.
Figure 18.11: Racetrack playa and the famous sailing rocks. (Left, Chloe Branciforte via Google Earth; Middle, CC-BY-SA 2.0; Gregory "Slobirdr" Smith Links to an external site.; Right, CC-BY-SA 4.0; Lgcharlot Links to an external site.)
Want to read more? Check out the article in PLOS ONE, an inclusive journal freely accessible to all. Norris RD, Norris JM, Lorenz RD, Ray J, Jackson B (2014) Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion. PLOS ONE 9(8): e105948. https://doi.org/10.1371/journal.pone.0105948 Links to an external site.