Porphyritic basaltic andesite (10.6 cm across) - this juvenile lava is sample from a 14 June 2006 block & 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 & pyroxene.
Locality: pyroclastic flow deposit at ~1200 meters elevation in the hamlet of Bebeng, village of Kaliadem, ~30 km from Yogyakarta, central Java, Indonesia (7º 34’ 57” South, 110º 26’ 51” East).
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One of the more recently active volcanoes is Mt. Merapi in central Java Island, Indonesia. Mt. Merapi has had frequent eruptions for at least the last 2000 years, with relatively quiet intervals at ~600-700 years ago & 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.
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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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