Mount Iriga is a stratovolcano whose most prominent feature is a large horseshoe-shaped caldera that is breached to the SE. It was formed by a massive volcanic landslide during an eruption that at one time was considered to have most likely occurred in 1628 CE, but was later found to have occurred earlier at some unknown time during the Holocene. The hilly terrain in the foreground, encloses small ponds on the surface of the debris-avalanche deposit. Photo by Chris Newhall (U.S. Geological Survey).