INTERPRETATION CALDERA STRUCTURE MODEL OF BATUR VOLCANO, BALI BASED ON GRAVITY ANOMALY

• Main Author: Sri Suryani, Meilani
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/42784
• Institution: Institut Teknologi Bandung

Indonesia located at active subduction zone which is part of ring of fire region. As a consequance, there exist many of volcano. Now Indonesia has 127 volcano and can be eruption anytime. One of volcano in Indonesia is Batur Volcano located in Kintamani, Bali. The current Batur Volcano is part of Ancient Batur Volcano which has erupted around 29.300 years ago and produce caldera I, and next big eruption was 20.150 years ago that produce caldera II and Batur Lake. Now, Batur Volcano have double structure caldera and the highest summit at 1.717 meter. Batur Volcano formed due to subduction of Indo-Australia plate beneath Eurasia plate. Plate subduction results in melting of the earth’s crust into magma. Before the magma comes out to the surface, magma accumulates in the earth’s crust forming magma chamber. Dimension of magma chamber and geological setting of volcano affect the scale of eruption. Geometry of magma chamber can be modeled and it can be used for study volcanic hazard potential. Gravity analysis used for subsurface interpretation. Model of subsurface be made from Complete Bouguer Anomaly print map Batur Volcano and do the digitation to get Complete Bouguer Anomaly digital map. And the result anomaly in Complete Bouguer Anomaly map is 75 – 150 mGal. Separation of local and regional anomaly using moving average method, produce local anomaly map -44 – 16 mGal. Low anomaly identified at summit area and inerpretate as sign of magma chamber in subsurface. Magma characteristic as liquid, andesite basaltic and have density 2,0 g/cc. Modelling 2,5D using background density worth 2,4 g/cc. Result of modelling show that magma chamber Batur Volcano is located at depth ±2.200 meter under sea level. Based on modelling, the oldest litology is tertiary rocks. Lava Cempaga deposit (? = 2,87 g/cc) and Lava Tejakula deposit (? = 2,68 g/cc). Exist normal fault structure that associate with caldera rim I and caldera rim II and can be identified because of discontinuity structure.