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Mount Pinatubo, Philippines

© CNES 1996 . Multispectral SPOT image | This image of Mount Pinatubo in the Luzon Island, the Philippines was taken in February 1996, several years after the eruptions of 1991 and 1992. It clearly shows the effects of such eruptions: a large fresh crater, volcanic material ejected on the slopes of the Pinatubo, and lahars (mudflows with volcanic boulders) filling up the valleys radiating out of the mountain.

Small explosions started on 2 April 1991 (after 400 years of quiescence) reaching the climax on 15 June. In early June, a lava dome began to grow on Pinatubo. The first powerful explosions started on 12 June raising an ash column 19 000 m, into the atmosphere. Explosive activities continued to destroy the dome and part of the summit and to produce pyroclastic flows, which as the image shows, mostly affected the north, northwest and west slopes of the volcano. Ashfall occurred over a large area. Climactic eruptions occurred on 14 and 15 June with a high eruptive column of ejected material which reached the stratosphere. A large part of this ash was spread over an extensive area including Manila by the tropical cyclone Yunya which passed south of Pinatubo on 15 June.

As the image shows a new 2 km diameter crater (which currently holds a lake) opened up but not at the same position of the pre-eruption summit. The estimated amount of material ejected is around 5 km3. The huge deposits of pyroclastics built featureless plain near the volcano. When the rainy season arrived in July 1991, lahars began to affect the major river valleys. All bridges near Pinatubo were destroyed, settlements buried, flood problems were recurrent. Lahars filling the river valleys and being a continuing regional threat are clearly identifiable on the image. All four major river systems were affected: the O'Donnell River in the north, the Sacobia River to the east, the Santo Tomas River to the southwest, and the Bucao River to the Northwest. The lakes next to the Santo Tomas accumulated part of the mudflow but even then enough material was present to create a depositional lobe at the coast. The pyroclastic material and the later mudflows down the Sacobia threatened the Clark Air Base which had to be abandoned. The image shows subsequent channelisation within the lahar filled river valleys which indicated that the threat remains.

© ESA 1996 . ERS-1 SAR Amplitude Image

More than 300 people perished and about 60 000 had to be evacuated. It is interesting that the pyroclastics and lahars reached the same areas as identified on basis of old volcanic deposits of Pinatubo which were thousands of years old. The aerosol which reached the stratosphere has been estimated to be between 20 and 30 megatons. This aerosol cloud spread rapidly in the stratosphere with temporary effects on the Earth's climate.