Atitlan y calderas.png

Natural history of Lake Atitlan

Central America, as part of the Pacific Ring of Fire, is geologically very active. Proof of this are the three giant calderas that can be detected today in the Atitlán area. 

 

The oldest, Atitlán I, identified with the help of satellite images, had a cycle from 14 to 11 million years ago. It was followed by Atitlán II, with a cycle of from 10 to 8 million years ago and the most recent, Atitlán III, is about 1.5 million years old and has had four huge eruptions.  

 

The last gigantic eruption left a large hollow and eventually collapsed the volcanic structures collapsed, filling some 300 meters of the caldera floor. Eventually the waters filled more than 300 meters of the ancient caldera. From the lake level to the top of the caldera is usually another 300 meters.

 

The eruption that formed the caldera is known as the Los Chocoyos eruption and it expelled up to 300 km3 of tephra. The huge eruption vaporized life in what is now Guatemala and dispersed ash over an area of about 6,000,000 square kilometers. This ash has been detected from Florida to Ecuador, and can be used as a stratigraphic marker in both the Pacific and Atlantic oceans (known as Y-8 ash in marine deposits) [8]. A chocoyo is a type of bird often found nesting in the relatively soft ash layer of the area's bluffs.

Volcanic features of the Lake Atitlan ar
Corte_y_mapa_Atitlán_caldera.png

After the eruption of Los Chocoyos, continued volcanic activity built up three volcanoes in the caldera. The Atitlan volcano lies on the southern edge of the caldera, while the San Pedro and the Tolimán volcanoes lie within the caldera. San Pedro is the oldest of the three and appears to have stopped erupting about 40,000 years ago. Tolimán began to grow after San Pedro stopped erupting and is probably still active, although it has not erupted in historical times.

 

Atitlán has developed almost completely in the last 10,000 years, it is the only active volcano in the area with eruptions in 1469 and between 1717 and 1721. It was also intermittently active between 1826 and 1856. Of these last eruptions, the only strong one occurred on May 3, 1853, when ash darkened the skies around the lake. Cerro de Oro is a young lava dome less than 5,000 years old.

 

On February 4, 1976, a major earthquake (magnitude 7.5) struck Guatemala, killing more than 26,000 people. The earthquake fractured the lake bed and caused the lake's subway drainage to lower the water level by two meters in one month.[9][10].

 

ECOLOGY

13 to 15 million years ago, the land bridge that united the South and North American continents emerged from the seas: Central America. (https://phys.org/news/2015-04-smithsonian-panama-debate-fueled-zircon.html). With the meeting of the arctic and the tropics, a varied and unique biodiversity developed with animals and plants from both continents. When humans arrived to the isthmus more than 12,000 years ago, they found a rich and diverse environment (https://www.the-scientist.com/features/the-peopling-of-south-america-67860).

 

The glaciations left behind a nearctic mountains of abundance surrounded by a sea of tropical life. In addition, the isolation of mountains and valleys facilitated the evolution of unique species of animals, plants and birds. In the lake basin, Nearctic life is found in the mountains bordering the lake to the north (pines, oaks, felines and deer) and Neotropical life is found in the southern volcanic foothills (corn, cacao, armadillos and monkeys).

 

Population growth and human activity has led to increased agricultural runoff and erosion, as well as a significant inflow of untreated sewage. The result is that the lake has changed from a crystal clear, nutrient-free (oligotrophic) lake to a turquoise lake with increased phytoplankton density and increasing bacterial contamination. In 2008 the first cyanobacterial bloom occurred [4]. Since then there has been monitoring of the water quality and increasing degradation has been documented with loss of clarity and increased phytoplankton density. 

 

Great American Biotic Intechange (GABI).
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