IntroductionThe caldera formed by the collapse of several overlapping stratovolcanoes east of Santa Ana volcano, and part of Santa Ana itself, during major rhyolitic pumice eruptions between 72,000 and 51,000 years ago. Deposits from these eruptions form a large layer present in most of southwestern El Salvador and parts of Guatemala.
Post-caldera eruptions produced basaltic cinder cones and lava flows near the western margin of the caldera and the about 6 rhyodacitic lava domes along a NE-SW line near the caldera lake margins.
The highest of the domes forms the wooded island of Isla de Cabra, or Cerro Grande. The youngest dome, Cerro Pacho, has probably formed less than 10,000 years ago.
from: Smithsonian / GVP volcano information
See also: Sentinel hub | Landsat 8 | NASA FIRMS