Atitlán / Toliman
One of the most beautiful places in the world was created by a series of giant caldera forming eruptions. The last one, about 84,000 bp, covered much of Guatemala with tephra (fragmental volcanic ejecta). An initial Plinian fall deposit mantled existing topography. It was followed by valley filling pyroclastic flow deposits, which comprise the bulk of the erupted tephra. The thick section of pyroclastic flows (the Los Chocoyos formation) is found all over the Guatemalan Highlands and much of the Pacific Coastal plain and. The caldera, now 25 km across, should be seen, not surfed.
Lake Atitlán fills a collapse caldera. Collapse accompanied the immense eruption of about 250 km3 of magma that turned into froth upon eruption and blanketed much of Guatemala with tephra fall and filled the low areas with flat-topped pyroclastic flow deposits. Whatever volcanoes existed before the eruption were collapsed into the developing caldera as the magma exploded out. During the last 84,000 yrs, four volcanoes have grown on the SW rim of the caldera.