Mojave Desert
While visiting California last summer, having never been to
a desert before, my family and I explored the Mojave Desert. Before arriving,
we did some preliminary research. The Mojave Desert is the driest and smallest
desert in North America. The Mojave is a very diverse desert with alluvial
fans, mesa tops, playa lakes and sand dunes. The Mojave Desert has a typical basin range and topography,
with the highest elevation point at 2000 feet and the lowest point at 280 feet
above sea level. The lowest point of the Mojave Desert is known as Death Valley;
the hottest place in all of North America. It is also home to 2500 different
plant and animal species, mostly known for it's native indicator species, the Joshua tree.
Deserts, in general, receive very little precipitation
annually, and due to the extreme dry air, experience, a quick evaporation rate.
There are three primary contributing factors to the creation of a desert; (1)
rain shadow effect, (2) plate tectonics, and (3) location; too far inland and
away from water supply. The Mojave Desert is surrounded by the Tehchapi
mountain range in the northwest, the Sari and San Bernadino ranges in the South, along with the Sierra Nevada mountain range. The surrounding mountain ranges block
precipitation from reaching the Mojave Desert, creating a rain shadow, therefore,
the Mojave Desert is a rain shadow effect desert. As clouds make their way up the
mountain ranges, the air becomes too dry and cold to hold the precipitation in,
resulting in one side of the range receiving the snow or rain, while the other
side of the range receives so very little precipitation that a desert forms.
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| This is a picture of Saline Valley, in Death Valley National Park. This picture illustrates how the Sierra Nevada mountain range acts as a rain shadow. https://www.nationalgeographic.org/encyclopedia/rain-shadow/ |
There are three stages to the formation of a
desert; early, middle and late stage. Each stage has unique characteristics associated
with it. In the early stages alluvial fans are created. Alluvial fans are the
result of sporadic torrential rainfalls that carry large amounts of sediment
from the canyons, or run off, which is left at the base of the mountain. The torrential
rain fall is typically short and fierce leaving most of the sediment load within
a small distance resulting in the creation of cone shaped formations, known as
alluvial fans, and seen in the picture below.
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Alluvial fans at base of Telescope Peak.
http://digital-desert.com/geology/alluvial-fans.html
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The alluvial fans can be so large that they
start to cover the mountain ranges and actually look a bit like a small mountain range themselves. Over time, during the middle stage of
desert formation, the alluvial fans begin to spread and connect with fans of
other nearby canyons, creating bajadas. Bajadas are known as aprons of sediment and are
the home to flat, silty, clay lake beds called playa lakes that are formed after rainfall. Because the evaporation
rate in a desert is so high, the playa lakes only last a few weeks. Specific to
Death Valley in the Mojave Desert, as the playa evaporates, borax or sodium
borate is created. This was of specific interest to my children, as borax is a
primary ingredient used to make homemade slime! Below is a photo of a playa
lake in the Mojave Desert, known as Soda Lake. Look closely and you will see the
encrusted salt formation (sodium borate) left behind during the evaporation process.
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Evaporate Crust - Soda Lake, Death Valley
http://digital-desert.com/soda-lake/
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By the late stages in desert formation, the many years of water
and wind erosion results in a flat plain or sediment filled basins with
isolated large rock formations known as inselbergs. The picture below shows the Mojave Desert native, Joshua tree with an inselberg in the background.
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Joshua Tree National Park - inselberg
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The Mojave Desert is rich in geologic history, offers so much to explore and provides
insight and understanding to all stages of desert development.
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