- Authors: Anastasia N. C. Purnamasari
- From: Environmental Science, Graduate School, Universitas Gadjah Mada
Abstract:
The eruption of Kelud volcano on February, 13th 2014 has produced a huge amount of material at the upstream of Bladak River. The materials are potentially becoming the flood material in downstream area. The mitigation efforts to minimize flood hazard require information of volume of the materials upstream. Moreover, information of physical characteristics of the materials are valuable for the community in the surrounding areas. Volume assessment and materials characterization were carried out through field measurements. The material volume assessment was done by using geophysical methods to estimate sediment thickness. The types of geophysical methods applied were microseismic method and seismic refraction. The results obtained from microseismic data processing was the value of natural frequency (f0) at each microseismic measurement point. The results obtained from seismic refraction data processing was the P wave velocity of sediment material, in which the derivative of P wave velocity will be calculated to obtain the S wave velocity. The S wave velocity is used to calculate the thickness of sediment combined with the value of natural frequency through the formula of h = Vs/4f0. The isopach line was produced through interpolation of sediment thickness measurement points. Later, the isopach lines were applied for volume assessment. Characterization of sediment material was done by calculating the percentage of pumice and non-pumice. The sediment material characterization data was processed manually by analyzing through field pictures. The data processing result were then analyzed descriptively. Materials thickness of pumice in land surface was analyzed according to slope classes. The result of volume assessment of the sediment materials at the upper stream of Bladak River was 27.6 million m3. The sediment at the upper stream of Bladak River consisted of 91.8% of pumice material. The pumice materials might be valuable for local economic generator as those materials have several uses, but should be investigated thoroughly through research. The community in the area surrounding Bladak River may exploit the materials for building materials or lightweight concrete materials, abrasive cloth jean or denim, etc. There were no significant correlation between land surface slope with the thickness of materials in the upper catchment of Bladak river.
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