The effects of the June 15, 1991, eruption of Mt. Pinatubo continue to
affect the lives of people living near the volcano on the island of
Luzon in the Philippines. The eruption produced a large amount of
volcanic debris that was deposited on the flanks of the volcano as part
of pyroclastic flows (avalanches of red-hot ash and pulverized rock). This perspective view looking toward the east
shows the western flank of the volcano where most of these pyroclastic
flows were deposited.
This debris consists of ash and boulders that mix with water after
heavy rains to form volcanic mudflows called lahars. Lahars are moving
rivers of concrete slurry that are highly erosive. They can sweep down
existing river valleys, carving deep canyons where the slopes are steep,
or depositing a mixture of fine ash and larger rocks on the gentler
slopes. The deposits left from a lahar soon solidify into a material
similar to concrete, but while they are moving, lahars are dynamic
features, and in a single river valley the active channel may change
locations within a few minutes or hours. These changes represent a
significant natural hazard to local communities.
The topographic data were collected by NASAs airborne imaging radar
AIRSAR instrument on November 29, 1996. Colors are from the French SPOT
satellite imaging data in both visible and infrared wavelengths
collected in February 1996. Areas of vegetation appear red and areas
without vegetation appear light blue. River valleys radiate out from the
summit of the volcano (upper center). Since the eruption, lahars have
stripped these valleys of any vegetation. The Pasig-Potrero River flows
to the northeast off the summit in the upper right of the image.
Scientists have been using airborne radar data collected by the
AIRSAR instrument in their studies of the aftereffects of the Mt.
Pinatubo eruption. AIRSAR collected imaging radar data over the volcano
during a mission to the Pacific Rim region in late 1996 and on a
follow-up mission to the area in late 2000. These data sets along with
remote sensing data collected from satellites provide valuable
information on the dynamic landscape and the hazards that it poses.