|The plate tectonics in the Philippines is complex and includes plate boundaries that are changing rapidly. Several micro-plates are getting squeezed between two convergent plate margins. Stratigraphic evidence indicates cessation and reactivation of subduction at some trenches. The currently active volcanoes in the Philippines define two north-south trending arcs. The scale and type of volcanism varies from monogenetic cinder cone fields to large stratovolcanoes and calderas. Composition of volcanic rocks range from tholeiitic basalt to andesite to shoshonite. Black triangles = active subduction zones with "teeth" on the over-riding plate, white triangles = inactive subduction zones with "teeth" on the over-riding plate, arrows = transform or major strike-slip faults, red triangles = volcanoes active in the last 10,000 years. Plates and micro-plates shown in different colors. Based on Divis (1983). Volcanoes from Simkin and Siebert (1994).|
In the west, more steeply east-dipping subduction of the Eurasian Plate (South China Sea basin and the transitional oceanic-continental crust of the Palawan block) along the 560 mile (900 km) length of the Manila and Sulu trenches produces a discontinuous line of active volcanoes from Taal in the south to Iraya in the north. Volcanism associated with this subduction zone began about 10 million years ago.
In the east, shallow west-dipping subduction of the Philippine Plate at the Philippine Trench produces a line of volcanoes from Balut in the south to Mayon in the north. Based on Divis (1983).
Volcanoes in an east-west zone across central Luzon may be associated with a "leaky" transform fault that connects the two subduction zones. The transform fault is offset to the right by the younger Philippine Fault. Based on Divis (1983).
The volcanoes of the Philippines are the most deadly and costly in the world. Fatalities have been caused by 13% of the historic eruptions, most notably at Taal and Mayon, and 22% of the eruptions caused damage. Mudflows are more common in the Philippines, compared to other regions, because of heavy rains. Tsunami are more commonly associated with eruptions at the Philippines than in any other volcanic region. Many of the Holocene volcanoes in the Philippines have eruptive products that have not been dated. Since the Philippines Institute of Volcanology and Seismology has been established the impacts of eruptions have been greatly reduced.
Sources of Information:
Defant, M.J., De Boer, J.Z., and Oles, D., 1988, The western central Luzon volcanic arc, the Philippines: two arcs divided by rifting?: Tectonophysics, v. 145, p. 305-317.
Defant, M.J., Dario, J., Maury, R.C., De Boer, J.Z., and Joron, J.-L., 1989, Geochemistry and tectonic setting of the Luzon arc, Philippines: geol. Soc. America Bull., v. 101, p. 663-672.
Divis, A.F., 1983, The petrology and tectonics of recent volcanism in the central Philippine islands, in Hayes, D.E. (ed.), The Tectonics and Geological Evolution of Southeast Asian Islands: Part 2, Amer. Geophys. Union Monograph.
Neumann van Padang, M., 1953, Philippine Islands and Cochin China. Catalogue of the Active Volcanoes of the World, International Association of Volcanology, 2, Rome, Italy, 49 p.
Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience Press, Tucson, Arizona, 349 p.
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