Death Valley is one of the driest places on earth but at
times it is subjected to heavy rainstorms. When it does
flood, one of the most dominant features of the Death
Valley landscape continues to form... alluvial fans.
When it rains in the canyon highlands each drop of water
strikes with full force on the bare earth jarring loose soil
and rocks. The rain water gathers volume and strength
as it travels down the canyons picking up more rocks and
debris, and with its abrasive load, scours out the narrow
canyon floor adding more material to the flow. As the
debris laden water is freed of the confines of the canyon,
it spreads out and seeks smaller and smaller channels.
In spreading out on its journey toward the valley floor the
water slows down and begins to release its load of silt,
sand, gravel and stones. Blocking of these channels by
the build up of rock material causes the water and its
debris to seek an easier route. Over a long period of time
paths are formed, plugged and formed again back an
forth across the fan evenly distributing the rock laod and
giving the fan its semicircular shape.
It should be emphasized that these alluvial fans are the
result of conditions and processes that remain active
today. They are not something that was formed eons ago
and are just sitting here weathering away. Alluvial fans
are a consequence of the thousands of years of continuing
erosion in the mountains - our lifetime is only a flicker in
the lifetime of this geologic feature.
Ths small alluvial fan directly in front of you is different
than most of the other fans in Death Valley. It's steeper
because its materials are derived from a hanging valley
and smaller because it is younger. Hanging valleys are
formed when uplift of the mountains takes place at a
more rapid rate than erosion allowing the rock debris to
pile up at a sharper angle. If no further uplift occurs
this fan will gradually extend itself farther out into the
valley and its steepness will eventually decrease.
Look around the edges of the mountain ranges that
surround Death Valley. How many alluvial fans in various
stages of formation can you pick out? Some of them
overlay each other and form a large alluvial apron around
the waist of the mountains. See how many you can spot
on your trip through Death Valley.