Abstract
Landslide is one of the geological phenomena that can be found frequently in Indonesia, where several areas are damaged due to landslide occurrence. One of it is located in Durensari Area, Bagelen, Purworejo, Central Java as the study area. The study area is characterized by the presence of altered volcanic rocks formed by the tertiary eruption, followed by hydrothermal alteration that contains clay minerals that could enhance the landslide occurrence. This study is conducted to identify hydrothermal clay minerals that which enhanced the landslide in the study area. Field mapping is done as field observation, as well as the clay minerals are identified from 10 samples using X-Ray Diffraction (XRD) as the study method. The observation has resulted that there are at least ±25 landslide occurrence points in the study area, which is associated with alteration type that consists of several clays, named by smectite, kaolinite, and illite assemblages as argillic alteration and chlorite, smectite, illite, and kaolinite assemblages as propylitic alteration. The research concluded that the replacement process of primary minerals by clay minerals and the presence of smectite affect the landslide occurrence in the study area, where moderate to the large landslide is associated with Argillic alteration, meanwhile small to moderate landslide is associated with propylitic alteration.
Highlights
Landslide is one of the most frequent hazards that happened in Indonesia
Field observation has resulted in about 30 location of past and present landslide event that related to clay mineral presence in the study area
The results show that several hydrothermal alteration clay minerals have been identified, such as smectite, chlorite, illite, kaolinite and mix clay minerals
Summary
Landslide is one of the most frequent hazards that happened in Indonesia. Ring of fire chain that lies from the north of Sumatra to Banda Islands and North Sulawesi produced volcanic rocks as well as producing hydrothermal activity. Hydrothermal fluid activity, in negative ways, could be altered and weaken the rocks. The weakened rock increased the landslide susceptibility. One of the areas characterized by its frequent landslide events can be found in Kulon Progo Mountains. The study area is administratively located in Durensari Area, Bagelen Subdistrict, Purworejo District, Central Java, Indonesia. The study area is characterized by its mountainous terrain, constructed by extrusive volcanic rocks and intrusive igneous rocks from the tertiary volcanic activity of Mount Ijo, one of three volcanoes identified in Kulon Progo Mountains [1,2]. The study area (Figure 1) is located about 40 km from Yogyakarta City
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