Most landslides occurring in Indonesia usually contain flow of debris and flood. It is getting riskier from year to year because landlides happen every year in the rainy season. Recently, the intensity of landslides is getting higher and wider, particularly in inactive volcanic areas. “This happens because the areas are mostly used for settlement and for economic activities,” said Ir. Amien Widodo, M.Si., faculty of Sepuluh November Institute of Technology, Saturday (26/3) in his doctoral exam at Auditorium of Faculty of Engineering UGM.
Amin mentioned that many researches about the cause of landslides in Indonesia have been conducted. However, the researches conducted simultaneously are very rare. Indonesia has abundant old quarter volcanic residue soil spreading in many places that have become dense settlements. This made Amien to conduct the research about slope stability of old quarter volcanic residue soil at Mt. Argopuro Panti in Jember.
Mt. Argopuro is one of volcanoes in East Java which is not active. Lava sediment of eruption is continuously getting thicker and physical chemical change that is softening. In his dissertation entitled The Role of Geochemistry on Slope Stability of Volcanic Residue Soil in Panti Area, Jember, East Java, Amien revealed that landslides occur in Breksi Argopuro and located at elevation about 400-800 m from sea surface and mostly in rubber plantation area. Landslide sector has an arched shape, width of landslide crown is more than 100 m at more than 25 m depth from road surface. Generally, it is formed by the clastic of Breksi Argopuro in more than 25 m thickness.
Amin’s research finding shows in landslide sector occurs silica-sesquosida anomaly which is disparaged to the deeper direction. Anomaly of CIA clastic index is over 85% up to the depth of 15 m. Besides, there is also anomaly of clay granule size more than 50% and anomaly of mineral content of halosite clay and organic substances met in each depth. “This phenomenon happens because of substance and material movement and weathering by water which passes the crack,” said the man born in Yogyakarta, 10 October 1959.
Standard Penetration Testing shows that weathering process of old quarter Breksi Argopuro has reached a depth more than 20 m from soil surface consisting of residue soil with a16 m thickness, weathered soil with a 4 m thickness and bed stone. “The water that flow in causes the lack of major substance in the 12 m depth,” he explained.
Mentioned by the husband of Isni Dwijuliati, S.E., geochemical process occurring along the crack has weakened the power of land shift. The geochemical process causes slope material old. “Old quarter volcanic residue soil at Mt. Argopuro can be said to be in a critical condition,” said the 1357th doctor of UGM who gained doctorate with honours.