Bulletin of the Geological Society of Malaysia, Volume 54, November 2008, pp. 97 – 102
1Institute for Environment & Development (LESTARI), Universiti Kebangsaan Malaysia, 43500 Bangi, Selangor, Malaysia
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2Department of Geology, University of Malaya, 50603 Kuala Lumpur, Malaysia
Abstract— At the Plio-Pleistocene transition, three large volcanic centres in the Bukit Barisan, Sumatera, began producing voluminous amounts of felsic tephra and pyroclastic flows. Field evidence at two of the centres suggests not one but multiple paroxysmal events spanning periods of up to almost 2 million years. At Toba (now Danau Toba, northern Sumatera) perhaps four such events occurred between 1.9 Ma and about 30 ka ago. The centres are marked by several hundred metres thick of ignimbrite, pyroclastic tuff flows, and air-fall tephra. All three eruption centres should be classed in the top rank of the Volcanic Explosivity Index (VEI).
Air-fall tuff has been identified at more than a dozen localities throughout Peninsular Malaysia as far east as the middle Lebir river, Kelantan, and in the upper Terengganu river reaches. Thicknesses are in the one-metre range. Recently all these Malaysian tephra have been attributed to one “Toba eruption” and assigned a 70-75 ka age ignoring the possibility of origins from the other two volcanic centres and brushing aside findings of detailed fieldwork and publications of pre-World War II vintage. Recently we studied the volcanic eruptives of the Maninjau volcanic centre in the Minang Highlands, western Sumatera, and here too evidence of multiple eruptions is present.
Keywords: distal tephra, multiple eruptions, Maninjau, Toba