Volcano-tectonic control of Merapi's lava dome splitting: The November 2013 fracture observed from high resolution TerraSAR-X data

• High resolution satellite radar data reveals lava dome splitting at Merapi volcano.
• New fracture has formed by phreatic explosion.
• Volcano is significantly changing its structural architecture.
• Lava dome splitting affects instability and volcano hazards.
• We discuss if crustal fault controls formation of a summit graben and development of volcano.

Volcanism at active andesite–dacite volcanoes is often associated with the formation and collapse of circular-shaped protrusions of extruded, highly viscous lava, the so-called domes, which are emplaced in the near summit region. Growing domes may experience stable and instable structural phases, with a gradual transition in between. Dome collapse and the break-off of instable blocks of viscous lava may lead to pyroclastic flows, one of the most lethal hazards at stratovolcanoes. At Merapi volcano, Indonesia, a new dome started growing in the summit region in the amphitheater formed in the course of the climactic 2010 eruption. Three years later, the dome reached a height of approximately 100 m and diameters of 220 and 190 m with a plateau-like surface area of 40,000 m2 approximately. On 18/11/2013, an explosion occurred without identified precursors, leaving a major fracture cutting the complete dome structure. Based on high resolution TerraSAR-X satellite radar imagery, we could identify the linear fracture, traceable over ~ 200 m in the long axis, up to 40 m wide. After geocoding of the radar amplitude imagery, the fractures azimuthal trend could be compared to other structural lineaments, indicative of a significant NNW–SSE structural direction that has formed on Merapi volcano in the past. The Merapi dome fractured in a NW–SE direction, and is consistent with the alignment of regional tectonic structures and of anticipated directions of pyroclastic flows. The fracture may be part of a larger volcano-tectonic system and may affect the dynamics and the stability of the Merapi dome.