Monitoring the Evolution of the Pasig-Potrero Alluvial Fan, Pinatubo Volcano, using a decade of Remote Sensing Data

Since the 1991 climactic eruption of Pinatubo in the Philippines, various hazards have affected areas surrounding the volcano. The most significant of these hazards involve the redeposition of pyroclastic flow and fall deposits as lahars, deposit-derived pyroclastic flows, and ash falls due to phreatic explosions. Many of these processes occurred in areas that are inaccessible for ground observation and monitoring. We describe here how sequential remote sensing data obtained over the period December 18, 1991, to November 1, 2001, from the SPOT, ERS, RADARSAT, SIR-C/X-SAR, AIRSAR, LANDSAT 7 ETM, and ASTER sensors provide a means of monitoring the decade-long development of the post-eruption Pinatubo landscape. This method represents an efficient and safe alternative to time-consuming, physically demanding and risky field campaigns. We apply principal component analysis, image subtraction, band ratioing, and density slicing to these data to track the changes in the post-eruption landscape, estimate volumes of deposition, and allow hazard vulnerability prediction along the timeline establish by the series of data sets. The maps derived from the remote sensing data agree well with the field derived maps for the first 5 years (1991-1995), provide important large-area coverage, and show details that are unobtainable from conventional ground-based mapping. The volume of lahars deposited during the first 6 months following the eruption is estimated between 0.045 and 0.075 km3, covering an area of ∼45 km2. Moreover, changes in the settlement patterns of the local population, as well as in the construction and modification of the engineering structures for controlling the lahar hazards, can be identified in the multi-temporal scenes spanning the entire decade of observations. These types of information are crucial inputs for local decision- and policy-making in volcanic hazard mitigation.