Lac Ilopango

Lake Ilopango is a crater lake which fills an 8 by 11 km (72 km2 or 28 sq mi) volcanic caldera in central El Salvador, on the borders of the San Salvador, La Paz, and Cuscatlán departments. The caldera, which contains the second largest lake in the country and is immediately east of the capital city, San Salvador, has a scalloped to high rim. Any surplus drains via the Jiboa River to the Pacific Ocean. The local military airbase, Ilopango International Airport, has annual airshows where international pilots from all over the world fly over San Salvador City and Ilopango lake. Four major dacitic–rhyolitic eruptions occurred during the late Pleistocene and Holocene, producing pyroclastic flows and tephra that blanketed much of the country. Tierra Blanca Joven eruption The caldera collapsed most recently sometime between 410 and 535 AD (based on radiocarbon dating of plant life directly related to the eruption), which produced widespread pyroclastic flows and devastated Mayan cities; however, a team of scientists concluded that the volcanic eruption might have happened in 431AD, based on volcanic shards taken from ice cores in Greenland, levels of sulphur recorded in ice cores from Antarctica, and radiocarbon dating of a charred tree found in volcanic ash deposits. The eruption produced about of tephra (several times as much as the 1980 eruption of Mount St. Helens), thus rating a 6 on the (VEI) Volcanic Explosivity Index. The "ash-cloud fallout ... blanketed an area of at least 10,000 square kilometers waist-deep in pumice and ash", which would have stopped all agricultural endeavor in the area for decades. It is also theorized that the eruption and subsequent weather events and agricultural failures directly led to the abandonment of Teotihuacan by the original inhabitants. Other researchers estimated that in its sixth-century eruption, Ilopango expelled the equivalent of of dense rock, making it one of the biggest volcanic events on Earth in the last 7,000 years.