Volcanism of the Philippines

The Philippines is a very volcanic island nation. There are between 23-53 active volcanoes at any time, another 30 potentially active volcanoes, and hundreds of inactive ones, and those are just the ones above sea-level. The eruptions of the volcanoes of the Philippines have been some of the most deadly and costly, having a great number of volcanic eruptions causing tsunamis and lahars. There are two major North-South volcanic arcs, one in Luzon, and one in Mindanao. At the moment, the six most active volcanoes in the Philippines are: Taal, Mayon, Bulusan, Hibok-Hibok, Pinatubo and Kanlaon.

 (map from PHIVOLCS)

PHIVOLCS (The Philippine Institute of Volcanology and Seismology) has been praised with being responsible for saving the most lives from volcano-related disasters in the Philippines. Before the 1951 eruption at Hibok-Hibok, which killed 3,000 people, there was no government agency in charge of dealing with volcanoes.

(photo from Hibok-hibokrocks.blogspot)
Today PHIVOLCS have a great site that has lists of active, potentially active, and inactive volcanoes. They include a series of definitions of volcano related phenomena (both direct and indirect), such as lahars, pyroclastic blasts, and tsunami-generation. They have several volcano monitoring stations (see my post on September 9, 2016, with a map of where these are). They monitor volcanoes through four main strategies: a seismic network, a ground deformation network, hot-spring temperature and flow-rate measurements, and visual observation.
PHIVOLCS uses a 0-5 Volcano alert system, where O means no alert/or quiet, and 5 means hazardous eruption in progress. They issue warnings for no fly zones in ares with high ash, as volcanic ash can damage airplane engines. They issue evacuation warnings and establish safety perimeters (from 4-9 kilometers depending on alert level between 1-4), they also issue warnings for ash fall in residential and farming areas. They are responsible for issuing warnings for riverside communities that could be affected by ash contamination in the water downstream of volcanoes, especially following periods of heavy rainfall.

(photo from Newhall, USGS)
The most recent eruption was on September 16, a 4-minute long phreatic (steam-blast) eruption at the Bulusan Volcano on the southeastern part of the island of Luzon (250 km from Manila). Bulusan regularly erupts these steam-blasts, which eject steam and ash into the air. Although some of the blasts are of short duration, the ash can be carried by the wind to nearby towns and water sources. Bulusan is a strato-volcano so people in the area take precautions because an eruption of Mount Bulusan could be highly explosive. Bulusan Volcano Natural Park surrounds the volcano, but there are evacuation procedures for nearby farms and PHIVOLCS establishes and adjusts the threat level as they evaluate the volcano. The alert level for Bulusan is currently 1, which means there is a low level of volcanic unrest. There is currently a four-kilometer Permanent Danger Zone around the volcano, and the area directly over the volcano is considered a no-fly zone during periods of any visible activity.

References: http://volcano.si.edu/reports_weekly.cfm#vn_273010, http://www.phivolcs.dost.gov.ph/index.php?option=com_content&view=article&id=50&Itemid=86, https://www.volcanodiscovery.com/philippines.html, http://hibok-hibokrocks.blogspot.com/2011/12/time-magazine-article-december-1951-mt.html, http://geographic.org/photos/volcanoes/volcano_photos_314.html