Post Eruption Hazards at Mt. Pinatubo, Philippines
Our project focused on the investigation of the post-eruption hazards at Mt. Pinatubo (Philippines) using remote sensing data, and field observations of the 1991 eruption deposits. Through the use of multiple satellite images, field work, and the 1996/2000 PacRim data sets, we conducted studies of the co- and post-eruption hazards of the volcano due to erosion and re-deposition of the extensive pyroclastic flow deposits.
During our project, volcanic hazards continue to persist at Mt. Pinatubo, more than a decade after the 1991 climactic eruption. Most obvious of these hazards are those involving the re-deposition of pyroclastic flow and fall deposits as lahars, deposit-derived pyroclastic flows and phreatic ash fallout. Many of these processes go unobserved when they occur in river valleys that have been inaccessible for several years after the eruption. In particular, these events occur in volumetric magnitudes, and at temporal frequencies, that make it difficult to identify in the field all of the changes that take place in many of the more remote pyroclastic deposits on the volcano.
A major part of this project was the assembly and analysis of a database of over 50 high resolution (1 - 50 dpixel) images that will facilitate this study. We collected Ikonos, SPOT, SIR-CK-SAR, Landsat, ERS, RADARSAT, and ASTER images of the area around Mt. Pinatubo. An example of the changes that could be seen in these data is shown in Figure 1. Our investigation focused on a retrospective analysis of the erosion, redeposition, and re-vegetation of the 1991 pyroclastic flow deposits of Mt. Pinatubo. The primary geologic goal of our work was the analysis of the spatial distribution and volume change of the sources and sinks of materials associated with mudflow (“lahar”) events. This included the measurement of river valley gradients and cross-sections using TOPSAR digital elevation data, as we are participating in the PacRim 2000 deployment to the Philippines specifically so that we can collect a second set of TOPSAR data that can then be used to create a topographic difference image of the volcano. The main results from this multi-sensor study have been published as Torres et al. (2004). A discussion of the methodology that we used to assemble an appropriate database was included in Mouginis-Mark and Domergue-Schmidt (2000).
As part of an educational outreach effort, we also helped the Philippine Institute of Volcanology and Seismology (PHIVOLCS) in the Philippines to use NASA data to study Mt. Pinatubo and other Filipino volcanoes. To help them, we conducted preliminary studies of other Filipino volcanoes, including Taal and Mayon. Ronnie Torres, who was initially a graduate student, and then a post-doc, supported under this grant, has been in the Philippines for almost the entire 12-month period. He has been working at PHIVOLCS, and has served a crucial point of contact between our NASA investigation and the on-going needs of local Filipino volcanologists.
