English: Mt. Merapi is an active subduction zone stratovolcano in the central part of Java Island, Indonesia. It's had frequent eruptions for at least the last 2000 years, with relatively quiet intervals at ~600-700 years ago and at ~1100-1400 years ago (see Gertisser & Keller, 2003). Between 20 and 30 eruption intervals have been recorded in the 1800s and in the 1900s. From May to June 2006, Merapi was observed to issue lava flows, ash columns, and ash flows.

The sample seen here is a porphyritic basaltic andesite - it's a juvenile lava sample from a 14 June 2006 block and ash flow (pyroclastic flow) from Mt. Merapi. Historically, most of Merapi’s lavas are basaltic andesites that are highly porphyritic (more than half the rock volume). Phenocrysts are commonly plagioclase feldspar and pyroxene.

Locality: pyroclastic flow deposit at ~1200 meters elevation in the hamlet of Bebeng, village of Kaliadem, ~30 km from Yogyakarta, central Java, Indonesia (07º 34’ 57” South latitude, 110º 26’ 51” East longitude)

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Some info. from:

Gertisser & Keller (2003) - Temporal variations in magma composition at Merapi Volcano (central Java, Indonesia): magmatic cycles during the past 2000 years of explosive activity.  Journal of Volcanology and Geothermal Research 123: 1-23.

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See info. at:

en.wikipedia.org/wiki/Mount_Merapi