Mount Iriga

Mount Iriga (locally known as Mt Asog) is a small andesitic stratovolcano that rises immediately W of Lake Buhi which has satellitic cinder cones of basaltic composition. A large breached crater open to the SE was formed as a result of a major debris avalanche that buried several villages and formed a broad hummocky deposit across the plain south of Lake Buhi. This catastrophic event was at one time considered to have occurred during 1628 CE, but later work has shown that the collapse occurred earlier at some unknown date during the Holocene. An older debris avalanche deposit of similar size was also described SW of the volcano (Paguican et al., 2010). Both debris avalanche deposits cover wide areas of low, waterlogged plains, to a distance of ~16 km for the older and 12 km for the younger. The collapse orientation and deposit constituents for both are consistent with being a response to transtensional faulting and gravity spreading. A cone and lava covering about 9 km2 post-date the younger collapse.