Studi Geomorfologi Kabupaten Kediri dan Pemodelan Bahaya Aliran Lahar Gunungapi Kelud

Abstract

Kelud Volcano (East Java) is an active volcano which often to occured the lahar flow. Lahar is a mixture of water and pyroclastic materials flowing down the river valleys. Historically lahar of Kelud often produced natural disasters, like in Kediri Regency, destroying everything through which it passed and claimed many lives. From 1990 eruption, for example, lahar of Kelud has killed 33 people and caused a lot of damages in Puncu and Plosoklaten Districts of Kediri Regency. Based on those disaster historical data, the lahar hazard studies of Kelud are needed to support disaster relief program and also for supporting development of Kediri Regency. This reasearch aims (1) to study geomorphology of the Kediri region and (2) to perform morphometric analysis of landforms for modeling lahar hazard generated from Kelud volcano. The method used is a geomorphological analysis (morphometry) using geographic information system (GIS). In lahar hazard assessment, the region is divided into two areas, namely proximal area and medial-distal area. The results showed that geomorphology of Kediri Regency dominated by volcanic and fluvial landforms. Fluvio-volcanic plains of Kelud Volcano is the largest landform that covers 52,44 % of Kediri region, while the smallest one is hilly volcanic landforms (0,06 %). The result of lahar hazard analysis showed that for proximal area, watershed of Puncu (Puncu District) and watershed of Mangli (Kepung District) were the most hazardous watershed to produce lahar, conversely watershed of Petungkobong (Ngancar District) was the lowest one. As for the medial and distal areas, Konto River (Kepung District) has the lowest value for lahar hazard, otherwise Sumberagung River has the greatest one. The hazard of lahar’s overflow for the medial and distal areas were located in along the vicinity of river valey, and it can be divided into two categories, i.e. high and moderate hazards. The categories were based on historical lahar disaster of Kelud in the past time. Another type of lahar hazard (BLP) was caused by the change of river slope, where the areas were situated up on coalescent laharic fans landforms, or at the points of break of slope from Kelud’s volcanic cone to fluvio-volcanic plains.