Author(s): Djoko Legono; Rachmad Jayadi; Adam Pamudji Rahardjo; Ani Hairani
Keywords: Snake line; Rainfall threshold; Lahar flow; Mt. Merapi area
Abstract: The lahar flow (or commonly termed as debris flow), is a fluid flow that contains water with a relatively high concentration of sediment. The lahar flow can generally take place in steep slope channels originated from mountainous area including active volcanoes. Mt. Merapi which lays at Java Island is one of many active volcanoes in Indonesia that erupts frequently and often accompanied with some amount of volcanic sediment produced by the activity and intensity of the eruption. The eruption of Mt. Merapi, depending upon its scale, may produce both primary disaster (such as pyroclastic cloud, ash fall, etc. ), as well as secondary disaster (debris avalanche and lahar flow). The lahar flow may occur as trigged by rainfall with certain characteristic, either its rainfall intensity and/or its rainfall duration. Previous researchers classified that the lahar flow or debris flow may be assumed as shallow landslide (Guzzetti, et al., 2008). This paper presents the results of the identification of snake line characteristics at some locations at Mt Merapi area. The snake line is the relationship between the rainfall intensity (I) and the cumulative rainfall (E) that recently used to examine the potential occurrence of lahar flow. These two parameters are also enable to be utilized to identify the rainfall duration (D). Previous workers were using the I-D relationship to describe the global threshold of the shallow landslide occurrence and lahar flow occurrence. However, the characteristics of the snake line has become similar important information for further development of lahar flow warning criteria.