is pinned between
the volcano San Salvador and Lake Ilopango Caldera. The Pacific Coast is adjacent south of the city Four major
dacitic–
rhyolitic eruptions occurred during the late
Pleistocene and
Holocene, producing
pyroclastic flows and
tephra that blanketed much of the country. The caldera collapsed most recently sometime between 410 and 535 CE (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 , 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 is estimated to have produced around of
ejecta (
DRE—several times more than the
1980 eruption of Mount St. Helens), which puts it at a rating of 6 on the
Volcanic Explosivity Index (VEI) and makes it one of the biggest volcanic events on Earth in the last 7,000 years. Fallout from the eruption column blanketed an area of at least with pumice and ash to a depth of at least , It was hypothesized that this eruption caused the
extreme weather events of 535–536 in Europe and Asia, but this is unlikely given the research published in 2020 that dates the eruption to 431 CE. == Scuba diving ==