Asphalt is an organic rock usually found in geological deposits, mostly associated with oil.
We mostly know it for its role in paving streets.
But sometimes, a geological occurrence can create the strangest lakes in the world: lakes of asphalt, which look like lakes from the space.
When subterranean bitumen (from which asphalt is mostly done) leaks to the surface, it creates a large puddle or lake, improperly called tar pits. By now, only on five places on Earth asphalt lakes have been found, all in the Western Hemisphere.
The largest asphalt lake is Pitch Lake (photos above), located at La Brea ("The Pitch" in Spanish) in southwest Trinidad Island (southern Carribean), 55 miles (90 km) from the capital Port-of-Spain. The lake covers about 40 ha and is 75 m deep, attracting annually about 20,000 visitors. It is mined for asphalt which is exported for high-quality road construction since the XIXth century. The origin of this lake is linked to deep faults in the connection with subduction under the Caribbean Plate of the Barbados Arc, which allowed oil from a deep deposit to be forced up millions of years ago.
The lighter elements in the oil evaporated, leaving
behind the heavier asphalt. The lake burbles, hisses and occasionally spits fire and its smell can be felt miles away, due to the sulfur which stinks like rotten-eggs.
The Trinidad Lake Asphalt Co exports $3 million worth of pitch annually.
In the asphalt, archaeologists found Amerindian pottery, along with the remains of prehistoric animals such as the mastodons and the giant sloth.
Asphalt lakes are areas of the death where many animals can get trapped and as they die, the asphalt preserves well their remains.
The lake holds reserves of six to ten million tons, which at the present rate of extraction would last for 400 years.
In Venezuela there's the second asphalt lake in the world: Guanoco (Bermudez) Lake (close to Macaraibo Lake), in the Orinoco basin.
The lake covers more than 445 hectares (1,100 acres) and contains an estimated 6,000,000 tons of asphalt.
It was used as a commercial source of asphalt from 1891 to 1935.
The third site where tar pits are found is The La Brea Tar Pits (Rancho La Brea Tar Pits), the famous cluster of small tar pits (one tar pit in photo center bellow) located in Hancock Park, in the urban heart of Los Angeles, California. Asphalt went up from the ground in this area for tens of thousands of years, reaching the surface on hundreds of sticky pools.
Methane gas also seeps up, causing bubbles which make the asphalt look like it's always boiling.
Asphalt and methane also appear under surrounding buildings, requiring special operations to remove it because it weakens the foundations of these buildings.
The "tar" pits were used as a source of asphalt (for use as low-grade fuel and for waterproofing and insulation) by early settlers of the Los Angeles area.
These asphalt pools have always been traps for animals and plants, which were well fossilized.
For science, they offered a detailed inventory of species dating from the last ice age. The trapping pools were sometimes covered with layers of water, dust, and leaves. The asphalt fossilized the bones of trapped animals, turning them into a dark brown or black color.
The asphalt also preserved very small "microfossils", insects, scorpions, crustaceans, wood and plant remnants, and even pollen grains, so scientists could rebuild vanished environments.
The oldest organisms entrapped in these tar pits were dated 38,000 years old.
Besides animals, in the pits was discovered a partial skeleton of a Native American woman, 9,000 years old.
Among the prehistoric mammals species found in La Brea Tar Pits, there are mammoths (the photo bellow shows a retrace of an entrapped mammoth), mastodons, giant bears, huge ground sloths (2 m high), the saber-toothed cat, ancient bison, camels, wild horses, American cave lions, tapirs, ancient pronghorns as well as many current species from North and Central America but also birds, turtles, fish, snakes, salamanders, frogs and toads.
The park's location in a major urban center, the history of dramatic discoveries, and excellent presentation in a museum built around the fossilized remains make the La Brea Tar Pits a famous and accessible archaeological site.
But there are two other asphalt pits with fossils in southern California: in Carpinteria, Santa Barbara County and McKittrick, in Kern County.