The
Atacama desert is found 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:
Salt
Lakes
During 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.
Snow
In 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.
Underground
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 to erupt.
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.
Where's the wettest place
on earth?
Does Anything Live There?
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
and 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 rainshadow.
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!
