Volcanic activity is reported to include seven volcanic centres, at least five craters and/or calderas up to 2 km in diameter, and a vigorous solfataric area at the highly altered volcanic dome structure.
One solfataric area emits a high-temperature (106 degrees C) plume to 30 m height with a roaring noise like a high-pressure geothermal borehole.
Images
The Smithsonian listing has a satellite photograph of the general area.
Geological Features
Mandalagan is part of the Negros Volcanic Belt.
Rock type is principally andesitic with some dacitic
A crater located near the center called "Tinagong Dagat", where hikers camp.
Eruption
The most recent eruption produced a thin basaltic lava flow, but it is not known when this is likely to have occurred.
Listings
Philippine Institute of Volcanology and Seismology (PHIVOLCS) lists Mandalagan as potentially active.
The Smithsonian Global Volcanism Program lists Mandalagan as fumarolic.