Date: Fri, 25 Nov 1994 20:20:43 MST From: "Patrick Allard 85.42"
Subject: Merapi eruption Short comment about the new eruption: Although precise information from VSI (Volcanological Survey of Indonesia) is still needed, the November 22 eruption may signify an important change in the location of future magma extrusion and the distribution of related hazards at Merapi. Over the past hundred years at least, glowing block avalanches, pyroclastic flows and lahars associated with extrusion of the lava domes were entirely confined to the W and SW flanks (last major eruptive phases in 1969, 1976, 1984 and 1992). Now, in 1979 (ref.1) and 1983 (ref.2) attention had been drawn on the potential risk of new magma outbreak towards the South (from the Gendol-Woro breach), that would threaten a more densely populated area including the northern suburb of Yogjakarta city. This concern was based on the following observations: increase and then persistency of very high temperatures in the Woro and Gendol fumarolic fields (implying a close proximity to the top of the magma column, as later verified from magnetotelluric measurements), appearance of scattered but new fumaroles on the Woro downslopes in 1979, and above all extreme fumarolic alteration of this sector of the edifice (weakening its stability or/and resistance to any magma intrusion). The present events seem to verify it, south-eastward migration of the eruption site being facilitated by magma blockage in the SW Batang breach due to the presence of the huge 1992-94 lava dome. References: 1. Allard P. & Tazieff H., Phenomenologie et cartographie thermique des principales zones fumerolliennes du Merapi (Indonesie). C.R. Acad. Sci. Paris, D-288, 747-750, 1979. 2. Tazieff H., Monitoring and interpretation of activity on Mt. Merapi, Indonesia, 1977-1980: an example of practical, civil defense, volcanology. In: Forecasting Volcanic Events (eds H. Tazieff & J-C Sabroux), Elsevier, Amsterdam, 485-492, 1983. Dr Patrick ALLARD Centre des Faibles Radioactivites, CNRS-CEA 91190 Gif/Yvette, France Tel. 33-1-69088542; fax: 33-1-69087716; e-mail:firstname.lastname@example.org