Slope movement and instability in Kanlaon Volcano, Philippines

Abstract:

Kanlaon is an active stratovolcano with at least 29 recorded eruptions since 1899. It is one of the few volcanoes in the Philippines with known debris avalanche deposits associated to it. The deposit is characterized by prominent hummocks distributed at least 300 sq. km. in the southwest side of the volcano. Stratovolcanoes are known to be inherently unstable due to numerous factors such as overburden, edifice discontinuities, basement structures and magmatic migration. Catastrophic debris avalanches are often the consequence of this instability.

Lineaments and collapse structures were mapped by interpreting a high-resolution topographic model of the volcano. Several arcuate scarp structures opening southwest towards the direction of the deposit are clearly seen, most likely the amphitheater from the debris avalanche. Most prominent are those near the summit, where more recent eruptions have overlain most of the amphitheater. In addition, clusters of N-S, NNW-SSE, and NE-SW lineaments are seen in the SE to the SW flank of the volcano, possibly a manifestation of spreading or downward movement to the south or southwest, where the debris avalanche deposits are.

InSAR time-series analysis using ascending ALOS PALSAR imagery acquired from 2007-2011 shows LOS range decrease at a rate of ~2 cm/yr in the western flank of Kanlaon near the summit. During this period, there was no eruption in the volcano, with the last an explosive phreatic eruption on June 2006, prior to the acquisition of the imagery. The gradual movement appears to be constrained within the old collapsed sector of the volcano and may be related to potential incipient flank instability controlled by edifice discontinuities.