Mode of Emplacement of Two Debris-avalanche Deposits at Banahao Volcano, Southern Luzon, Philippines

概要

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A detailed investigation reveals that a large-scale debris-avalanche deposit at Banahao volcano in the southwest Tagalog province, Luzon Island resulted from two discrete edifice-collapse events. The two avalanche deposits (Lucena and Lucban) are discriminated mainly on the basis of differences in: (1) hummock size and dislribulion, (2) block size and degree of deformation, (3) percentage of matrix material, (4) petrography and chemistry of rock constituents, (5) presence of juvenile fragments, and (6) related secondary lahar deposits. The Lucena debris avalanche deposit was derived from a large-scale collapse directed towards the southeast and was apparently accompanied by a magmatic eruption. A repose period of considerable duration, followed by cone building within the remnant amphitheater, occurred before the emplacement of a smaller second avalanche (the Lucban avalanche) to the northeast. The avalanches travelled approximately 26 and 13 km, and their volumes are 4 km^3 and 1 km^3. Height to length ratios (H/L) for both the Lucena and the Lucban avalanche deposits were estimated at 0.06.
特定非営利活動法人日本火山学会の論文
1994-07-20