Hot Pyroclastic Deposit As Lahar Resistor:
A Case Study Of Gendol River After The Mt. Merapi 2010 Eruption
Author(s)
S. Sandy Putra, C. Hassan & S. Hariyadi
Abstract
Hot pyroclastic deposit as lahar resistor:
a case study of Gendol River after the
Mt. Merapi 2010 eruption
S. Sandy Putra, C. Hassan & S. Hariyadi
Research Centre for Water Resources, Indonesia
Abstract
The year 2010 left unforgettable memories for Indonesian people because of the
Mega Eruption of Mt. Merapi, which was predicted as the biggest eruption since
1870. Lahar became a dangerous secondary hazard around the Mt. Merapi
watershed. The lahar event record until February 2011 in Gendol Watershed
showed less instances of lahar occurrence compared with other areas, such as
River Putih WS (>10 events), River Apu WS (>5 events), etc. This paper
provides literature analysis, stratigraphy study analysis, and also temperature
measurement reports, in association with lahar triggered factors in the Gendol
Watershed. Previous stratigraphy survey data on Gendol River (Newhall et al.,
Journal of Volcanology and Geothermal Research, 2000) shows that the
pyroclastic deposit material allows water infiltration because of its porosity. The
conditions of a deep clay (impermeable) layer and no water table found up to
±11m depth support rain water infiltration. The post eruption pyroclastic deposit
is still at a high temperature (±105°C), which causes some infiltrated water to be
evaporated. Less runoff will promote a smaller amount of sediment transport and
less risk and lower destructive force of a lahar event. Over a sufficient period, the
pyroclastic deposit will be consolidated and compacted as a result of the
cementation process of active pyroclastic elements (solidified by chemical
bonding). Hot pyroclastic material in the Gendol River after the Mount Merapi
Eruption 2010 could have acted as a resistor for lahar. The resist period was
±145 days, from the first eruption until the significant lahar event. The influential
resistance factors are thickness, density, porosity, riverbed gradient, rain
intensity, and temperature of the pyroclastic deposit. It gives enough time for
urgent action (human relocation), environment mitigation, reconstruction, and
remediation in the watershed. This fact was the empirical basis for the
Keywords
Merapi, eruption 2010, pyroclastic, temperature, lahar resistor
Related Book
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