The last major eruption on Galunggung was in 1982, which had a Volcanic Explosivity Index of 4 and killed 35 people. On the southeast slope of Galunggung Volcano on the densely populated island of Java, a hummocky deposit called the Ten Thousand Hills of Tasik Malaja drew the attention of Europeangeologists in the early part of the 20th century. Dutch geologist B.G. Escher hypothesized that a breakout of a crater lake resulted in a watery landslide that formed the deposit. The hummocks were likely material left behind as the more watery parts of the slide flowed away. Austrian geologist F.X. Schaffer suggested that the hummocks might be manmade; as the local people cleared the land to make ricefields, they made dumps of the boulders and cobbles that they found. The dumps became hummocks, and were used as sites for homes and fruit trees, as they offered protections from hostile people as well as from the mosquitoes and rats of the rice fields. Schaffer noted that the volume of material might seem large for "occidentals but it is not beyond the powers of the numerous and industrious Malays."
The horseshoe shape of Galunggung's crater and the nature of the hummocks, however, suggest a different cause for the formation of the Ten Thousand Hills. Since 1980, geologists from the Volcanological Survey of Indonesia and the U.S. Geological Survey have reinterpreted the deposit as a debris-avalanche deposit. Quarry exposures show pieces of the old volcano -- the block facies -- shattered but intact, that are similar to the deposits at Mount St. Helens and Mount Shasta. Radiocarbon dates of a lava flow within the deposit show that the debris avalanche is less than 23,000 years old.
Galunggung was originally a stratovolcano known as Guntur volcano (+2168 m).
The Northwest striking lineaments and the fracture zone in the 1982-83 cinder cone are parallel to the Sumatera fault system, while the fracture zone in the 1918 lava dome and dikes position are similar to the principal stress derived from Indian ocean plate movement.
Galunggung lava flows, lava domes, dikes and volcanic bombs, are basalt or basaltic andesite in composition and have porphyritic textures with medium-sized phenocrysts in fine-grained or glassy groundmasses.
Share your thoughts, questions and commentary here
Want to know more? Search encyclopedia, statistics and forums:
Press Releases |
The Wikipedia article included on this page is licensed under the
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m