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Some of
the world’s strangest lakes are filled not with water but with asphalt,
also known bitumen, the same material that roads are paved with.
The great majority of asphalt that is used today is derived from
petroleum, but asphalt is also found in concentrated form in nature.
Sometimes they seep from the ground and creates large puddles known as
tar pits or asphalt lakes. At other times, they are found soaked in
sands, as in Athabasca oil sands in northeastern Alberta, Canada, which
is the world’s largest deposit of natural bitumen. Asphalt is also known
to erupt in underwater volcanoes, but these are relatively rare and were
discovered only in 2003.
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There are only a few known large asphalt lakes around the world. The
largest of these is located in the village of La Brea in southwest
Trinidad, and is called the Pitch Lake. The lake covers about 40
hectares and is reported to be 75 meters deep. The liquid asphalt is so
thick and viscous, that the surface can be walked upon. But if you stand
on the surface for too long, you will slowly sink into it. Although the
lake appears quiescent the asphalt is slowly moving and you can see flow
lines on the surface. As the tar moves, sometimes prehistoric trees and
other objects that have fallen into the lake appears, then disappears
and then reappears again.
The lake was created thousands of years ago by the process of subduction
when the Caribbean continental plate was forced under another plate.
This opened fault lines that allowed crude oil from deep underground
deposits to rise to the surface, where it collected in a volcanic
crater. The air caused lighter elements of the oil to evaporate, leaving
behind the heavy asphalt, a mix of oil, clay and water.
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The lake was discovered in 1595, and has been commercially mined since
1867. An estimated 10 million tons of asphalt has been extracted from
the Pitch Lake so far. About 6 million tons of asphalt is still left.
The La Brea Pitch Lake is also a tourist attraction and brings about
20,000 visitors annually. Sometimes people swim in the waters of the
pitch lake because they believe it has therapeutic properties.
Another famous asphalt lake is located in urban Los Angeles. It’s
actually a group of pits called the La Brea Tar Pits. Don’t be confused
by the name. “Brea” is just a Spanish word for asphalt. There are other
tar pits in southern California such as the McKittrick Tar Pits in Kern
County and Carpinteria Tar Pits in Santa Barbara County. Elsewhere,
there is Lake Bermudez, in Venezuela, which is the world's second
largest natural tar pit. Tar pits have also been found in Iraq and in
Baku, Azerbaijan.
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In addition to geologists and oil barons, asphalt lakes are objects of
interest for naturalists and paleontologists too as well, because hidden
beneath the sticky, gooey layers are remains of unimaginable amount of
prehistoric life. Over thousands of years these lakes have swallowed
saber-toothed cat, dire wolves, bison, horses, turtles, snails, clams,
millipedes, gophers, mammoths and hundreds of other species of
vertebrates and invertebrates. These animals had wandered too far
looking for food perhaps, and became trapped in the asphalt. The trapped
animals attracted predators who became stuck as well as. Death came
either by suffocation or hunger. It’s a terrible way to die, but a
fantastic way to preserve fossils.
A surprisingly large percentage of fossils recovered from tar pits — as
high as 90 percent—are that of predators. The most common large mammal
recovered from La Brea pits, also known as Rancho La Brea, is the dire
wolf with more than 4,000 specimens, followed by saber-toothed cats with
over 2,000 individuals. Coyotes rank third. Even most of the bird
fossils are predators or scavengers, such as vultures, condors, eagles,
and giant, extinct, storklike birds known as teratorns.
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Aside from animals, tar pits have also preserved prehistoric wood and
vegetation. But the most unexpected find is that of a woman, dated at
approximately 10,000 years. The skeleton was accompanied by the remains
of a domestic dog. Researchers believe the death might have been
ceremonial or a sacrifice, just like sacrifices made in peat bogs.
Originally, the bones recovered from the pits were dismissed as recent
deaths. It was not until 1901 when a geologist visited the tar pits and
identified the bones belonging to many extinct species that the
scientific community began to take notice. Between 1905 and 1913 amateur
fossil hunters took away millions of bones from the pits before the
landowner, George Alan Hancock, fearing the fossils would be lost for
ever, put an end to it. He then granted exclusive rights to excavate the
fossils to the Los Angeles Natural History Museum, but only for two
years. Between 1913 and 1915, the museum collected about a million
bones. Hancock later donated the pits to the county, on the condition
that they be preserved and appropriately displayed. Some of the fossil
specimens are now displayed at the nearby George Alan Hancock Museum.
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There is still at least one actively excavated pit in Rancho La Brea. |