Volcanic shape and structure

This volcano has a very big shape compared to G.Merapi that has a very slim shape, G.Merbabu seems more like 'overgrowth' volcano. Summit area can be divided into three parts as remnant of volcanic graben : Sari graben has ESE-WNW direction, Guyangan graben with SSW-NNW direction, and Sipendok graben has WNW-ESE direction. These graben have radial direction from the summit, made the body of G.Merbabu as if cut off volcano. Flank eruption of G.Merbabu mostly produced lava flow and pyroclastic flow. Lava flowed through the eruption points and covered by pyroclastic flow and pyroclastic fall. The eruption points interpreted extend along fault zone that has NNW-SSE direction across summit area, assumed as normal fault called Tempel fault and Telomoyo fault. These eruption points also formed a lineament continuously through G.Merapi. At G.Merbabu also appeared several craters, known as Old Merbabu, Young Merbabu, Banci, Puasa and Kumbang. Inside Young Merbabu crater found another smaller craters called Manuk crater, Candradimuka crater and Sambernyawa crater. Inside Banci crater also found Lirang crater. These craters have diameter about 125 m to 1350 m.  

General geology

Morphology of G.Merbabu can be separated as:

• Morphology of graben remnants (summit area), consist of three parts as Sari graben, Guyangan graben, and Sipendok graben. The all three grabens predicted as volcano-tectonic activity remnant, where tectonic activity appeared as faulting followed by eruption activity and flank eruption formed flank eruption cone.
• Morphology of summit area, formed by several peaks of G. Kukusan, G.Pertapan, G.Pregowati, G.Kenteng, G.Pregodalem, and G.Watutulis. These cones formed Merbabu crater structure, consist of lava rocks.
• Morphology of volcano body, predominance of all the body of G.Merbabu , which make G.Merbabu has a very large shape.
• Morphology of wavy hills, situated at west part formed by pyroclastic rocks.
• Morphology of flank eruption points, situated surrounding the summit formed a lineament of NNE-ESE direction. This morphology formed by two flank eruption Kumbang and Puasa located at the north of G.Merbabu summit, dominantly by lava flows.
• Morphology of volcanic hills remnant, consist of G.Telomoyo, G.Gajahmungkur and G.Andong, formed by lava.
• Lowland morphology formed by lahar and old pyroclastic flow deposits.

Generally G.Merbabu volcanic products can be divided into two groups; G.Merbabu products and G.Merbabu surrounding area products. G.Merbabu volcanic products consist of primary deposit from central and flank eruption, and secondary product as lahar deposit. Primary deposit produced from three craters; Old Merbabu crater, Young Merbabu crater and Banci crater. Flank eruption produced from Puasa crater and Kumbang crater. Volcanic product from G.Merbabu surrounding area consists of deposits from G.Sadang, G.Telomoyo-Andong, G.Merapi and Tertiary sediment rocks.