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The Physical Geography of Southeast Asia$
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Avijit Gupta

Print publication date: 2005

Print ISBN-13: 9780199248025

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780199248025.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 17 June 2021

Volcanic Hazards in Southeast Asia

Volcanic Hazards in Southeast Asia

(p.250) 15 Volcanic Hazards in Southeast Asia
The Physical Geography of Southeast Asia

Jan J. Nossin

Oxford University Press

Active volcanism in Southeast Asia is associated with marked zones of activity in the Earth’s crust that run through south and east Indonesia and the Philippines. These zones are also characterized by frequent earthquakes and a measurable movement of tectonic plates, often in the order of 5 cm yr−1. The underlying mechanism is that of subduction of oceanic plates below continental plates; the rigidity of the moving plates causes ruptures and shockwise adjustments (earthquakes). The oceanic plate, while being under thrust, sinks down to great depths below the continental plate and in the process loses its rigidity owing to heating and part assimilation into the underlying magma. Earthquakes are caused in the zone where the subducted plate is still rigid. Chapter 1 in this book puts this phenomenon in the regional context. Volcanism in this zone is marked by frequent eruptions, mostly violent and of an explosive nature. It is manifest in distinct belts that comprise all (or nearly all) of the Philippines, and large parts of Indonesia with the exception of, roughly speaking, Kalimantan and Papua. The violence of the eruptions poses threats to human settlements in the surroundings of the volcanoes, to the cultivated lands, and the infrastructure. These threats may occur during and after the actual eruption, and they may indirectly cause other hazards as well. Moreover, volcanoes in apparent dormancy that have not erupted in historical times may still come to life as the interval between eruptions may be very long. In the present chapter these hazards will be discussed. Natural hazards have been defined in four ways, of which the 1982 definition of the United Nations Disaster Relief Co-ordinator (UNDRO) seems appropriate to follow in the context of volcanic hazards (Alexander 1993). UNDRO defines natural hazards as ‘the probability of occurrence within a specific period of time and within a given area of a potentially damaging phenomenon’. A hazard therefore may represent a situation with the possibility of a disaster that may affect the population and the environment which are in some degree of vulnerability.

Keywords:   atmospheric effects, base surge, crater lake, dome collapse, flood, hazard zonation, lakes, magma plug, natural hazards, plate tectonics

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