Mount Iriga, also known as Mount Asog, is one of the active volcanoes in the Philippines in the province of Camarines Sur. It is known for its phreatic (water) explosions. It is also a stratovolcano of about a kilometer from Lake Buhi. It rises 1,196 m (3,924 ft) with a base diameter of 10 kilometers. The volcano is dominantly andesitic in composition, but has several basaltic flank cones. It has a large crater breached to the SE, which formed during a massive flank failure that produced a large debris avalanche which buried several villages and formed a hilly, irregular deposit on the plain south of Lake Buhi 4 km from the summit.
Iriga is part of the Bicol volcanic arc which comprises at least 12 volcanic vents and complexes and is one of the 3 historically active, but the least active centers of the arc (the other 2 being Mayon and Bulusan). Iriga has only 2 known recorded eruptions in historic times. The catastrophic debris avalanche of Iriga volcano had been believed to have occurred during the 1628 AD eruption, but later work has now shown that the collapse and eruption occurred earlier at some unknown date in the past few thousands years. The avalanche was followed by phreatic explosions that created a small crater at the base of the scarp.
Lake Buhi is a large shallow lake of 18 km2 surface near Iriga volcano and lies in the valley formed by the 2 older Mt. Asog and Mt. Malinao volcanoes. . It has an average depth of 8 meters. It has probably been crated by the an earthquake in 1641, when a portion of Mt. Asog collapsed to form a natural dam. The lake is famous as one of the few lakes that contains the sinarapan (Mistichthys luzonensis) which is the world’s smallest commercially-harvested fish.