Mount Bulusan, or Bulusan Volcano, is the southernmost volcano on Luzon Island in the Republic of the Philippines. It is situated in the province of Sorsogon in the Bicol region, 70 km (43 mi) southeast of Mayon Volcano and approximately 250 km (160 mi) southeast of the Philippine capital of Manila. It is one of the active volcanoes in the Philippines.
Bulusan is classified by volcanologists as a stratovolcano(or a composite cone) and covers the northeast rim of Irosin caldera that was formed about 40,000 years before present. It has a peak elevation of 1,565 m (5,135 ft) above sea level with a base diameter of 15 km (9.3 mi).
Located around the mountain are four craters and four hot springs. Crater No. 1, called Blackbird Lake, is 20 m (66 ft) in diameter and 15 m (49 ft) deep. The oval Crater No. 2 is 60 by 30 m (200 by 98 ft) and 15 m (49 ft). Crater No. 3 is about 90 m (300 ft) in diameter and 20 m (66 ft) deep and Crater No. 4, which is near the northeastern, rim opened during the 1981 eruption. There is also a 100-metre (330 ft) fissure measuring 5 to 8 m (16 to 26 ft) wide below Crater No. 4.
Its hot springs are San Benon Springs, Mapaso Springs, San Vicente Springs, Masacrot Springs. Its adjacent volcanic edifices are Mt. Homahan, Mt. Binitacan, Mt. Batuan, Mt. Calungalan, Mt. Calaunan, Mt. Tabon-Tabon, Mt. Juban, and Mt. Jormajan.
Bulusan is generally known for its sudden steam-driven or phreatic explosions. It has erupted 15 times since 1885 and is considered as the 4th most active volcano in the Philippines after Mayon, Taal, and Kanlaon.