Atacama desert is nestled along the coast of Chile, South America -
right next to the Pacific Ocean - the biggest body of water in
the world. Much of the desert extends up into the Andes mountains and
is very high in elevation. Unlike more familiar deserts, like the Sahara
desert in Africa and the Mojave in California, the Atacama is actually
a pretty cold place, with average daily temperatures ranging between
0°C and 25°C. The annual rainfall (or lack of it) defines
a desert, but that doesn't mean that it never rains in Atacama. Every
so often a warming effect over the Pacific Ocean around the equator
changes the weather the world over and even places like the driest desert
in the world can become doused with drenching storms. Even though Atacama
gets almost no rainfall, there is water in this arid place and you'll
find it in the following places:
years of heavy rainfall in the distant past, enough water accumulated
in basins found throughout the Andes to create lakes. Some of the lakes
got their water from melting glaciers at the end of the last ice age.
But in some lakes in the Andes mountains, such as Atacama, more water
is lost through evaporation than is replaced by rainfall so the lakes
are drying up. As the water evaporates, the mineral salts in the water
become more concentrated, creating very salty water.
the higher elevations when precipitation comes to Atacama snow falls
instead of rain. There are small patches of unmelted snow in the mountain
tops where in never gets warm enough to melt the snow.
Anywhere you go
in the world, regardless of how much or little it rains, there is always
water underground. After it rains, some of the rainwater evaporates
back into the air, but much of it trickles down into the ground and
stays there - even in the desert. How much water and where depends on
a number of things; soil composition, air and soil surface temperature,
amount and frequency of rainfall/precipitation, and drainage. Since
the Andes is a volcanically active mountain range, the magma beneath
the ground will heat the groundwater in certain places causing geysers
Fog and Dew
Most of the precipitation that comes
to the Atacama is in the form of fog that blows in the from the Pacific.
Fog is essentially very low clouds, consisting of water vapor cooling
and beginning to condense. If you've ever been in fog you know that
it can leave you a little moist. When the air temperature reaches dew
point the water vapor in the air condenses to leave little droplets
of water behind. The few things that are able to survive in the Atacama
live on the combined moisture from fog and dew.
Many people have
the view that deserts are places forsaken by Mother Nature and that
no living thing would possibly want to set up camp in a place so dry.
Although it is tough to find anything living in the Atacama there are
isolated pockets and small patches of plants, which support life for
animals and insects. Some plant species have adapted well to this dry
environment by developing tap roots that run very deep into the ground
gathering water from below. There are flocks of flamingos that live
in and around the salt lakes feeding on red algae that grows in the
waters. There are even people living in the Atacama.
There is a town
called Calama in the desert which is complete with motels, restaurants
shops, but it is
definitely not the norm. For the most part, Atacama is a pretty lonely
place. Humans have lived in the Atacama for many thousands of years,
based on the cultural relics and artifacts that archaeologists have
found. The South American Indians who have set up housekeeping in the
desert over the millennia have left relics from their culture and even
themselves. Because the Atacama is so bone-dry the bodies of the buried
indians have dried perfectly preserved turning them into mummies. Some
of the oldest mummies found anywhere on earth have come from the Atacama
Desert and have been dated to be 9,000 years old!
What Causes Deserts?
One reason is that
the high atmospheric pressure in this region over the Andes can cause
dry, cold air from the upper altitudes to compress and come down to
earth. This dry air has almost no water vapor so it can be easily heated
by the sun, causing high ground temperatures with very low humidity.
Another reason that
the Atacama doesn't get enough rainfall is because of a phenomenon called
The warm, moist tropical air that blows on the tradewinds from the east,
which douse the South American rainforest, get hung-up on the east side
of the Andes. The mountains are so high in altitude that the air cools,
condenses and rains (or snows) on the mountains. As the air descends
the other side of the mountain range it warms, holding in its moisture
preventing rain from falling on to the ground below.
This is one of the
reasons why the Amazon basin and river are the largest anywhere in the
world. The mountains that cause the Amazon
to be the largest river from collecting all the rainfall are also
responsible for preventing the Atacama from ever receiving any rainfall.
The driest and one of the wettest places in the world are right next
to each other!