IDENTIFICATION OF PYROCLASTIC DEPOSIT TYPES (FLOWS, SURGES AND FALLS) AT MERAPI VOLCANO AND FACTORS INFLUENCE THEIR DISTRIBUTION

Convention Bandung 2004 (CB2004)
The 33rd Annual Convention & Exhibition 2004

Indonesian Association of Geologist
Horizon Hotel, 29-30 Nov, 1 Oct 2004, Bandung

IDENTIFICATION OF PYROCLASTIC
DEPOSIT TYPES (FLOWS, SURGES AND
FALLS) AT MERAPI VOLCANO AND
FACTORS INFLUENCE THEIR
DISTRIBUTION

Supriyati D. Andreastuti

Volcano Technology Research Center (BPPTK),
Directorate of Volcanology and Geological Hazard Mitigation

Abstract

Identification of pyroclastic deposit types (pyroclastic flow, surge and fall) was
made in the field using physical characteristics (internal structure, thickness,
colour, lithology and mineralogy) and analysed further by grain size analyses.
Pyroclastic flow deposits are composed of ash to block sized material, and are
depleted in ash (less than 2 %). Pyroclastic surge deposits are dominated by
ash material, range from fine to coarse ash, and are fine-ash-enriched (up to 17
%). Pyroclastic fall deposits are characterised by a wide range of grain-sizes
from fine ash to lapilli and are generally depleted in fine ash.

Distribution of these deposits was influenced by topographic condition
(roughness and orientation) and grain size. In pyroclastic surge, the more
irregular the morphology the shorter the travel distance from the source.
Perpendicular topography passed by the surge also result in shorter distance
than the parallel one. Pattern of prevailing wind and strength of wind condition
affects the shape of the dispersal and distribution pattern of fine grained
material of pyroclastic fall leading to climate condition of eruption can be
suggested.

Geo-Environment & Hazard