History of Lake Atitlan
Lake Atitlan is the deepest lake in Central America and one of the most beautiful lakes in the world. "Atitlan" in Mayan means "the place where the rainbow gets its colours".
The lake is situated in an area of Guatemala where a string of volcanoes have formed as the Cocos plate of the Pacific is sub ducted beneath the Caribean plate.
150,000 years ago a magmatic batholith (a huge subterranean pocket filled with liquid magma) formed in the area that is now the lake. This was fed by the Los Chocoyos Batholith, which 84,000 years ago, after years of building pressure, finally discharged in a violent expulsion of over 250 cubic km of magma, ash and sand.
The eruptive column reached heights of 40-60km and dispersed ash over an area from Florida to Ecuador.
So much magma had been expelled that only an empty cavity remained. Unable to support the weight of the earth above it, the area collapsed, forming the 18km diameter caldera. Originally 900m deep, the caldera filled over time with rainwater and sediment to create the lake we have today. The caldera is lined with sediment for 300m or so, before being filled with water for another 340m.
Since the major 
eruption three new volcanoes have formed on the southern boundary of the lake; volcanoes San Pedro, Toliman and Atitla n.
San Pedro stopped erupting 40,000 years ago. Toliman began growing after San Pedro stopped erupting. It remains active, but has not erupted in historic times. Atitlan last erupted in 1853 when ash darkened the sky for hours.
Seismic activity has been low in the last decade, but volcanic activity does influence relatively long-period fluctuations in the lakes level. Reportedly low in the 1820s, it rose by 10-15m in the 1870s before dropping in the 1920s and rising again from the 1940s until present.
These changes are caused by annual rainfall which can account for rises of up to 3.3m as seen in 1933, and regional earthquakes affecting the lakes underground drainage, such as in 1976 when the level dropped 20m. It is thought further changes are caused by a rising and falling of the silt layer at the bottom of the lake, caused by cycles of volcanic activity and inactivity, in what may be a 50-60 year cycle.
