Overbank block-and-ash flow deposits and the impact of valley-derived, unconfined flows on populated areas at Merapi volcano, Java, Indonesia

Gertisser, Ralf, Cassidy, Nigel, Charbonnier, Sylvain, Nuzzo, Luigia and Preece, Katie (2012) Overbank block-and-ash flow deposits and the impact of valley-derived, unconfined flows on populated areas at Merapi volcano, Java, Indonesia. Natural Hazards, 60. pp. 623-648. ISSN 0921-030X

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Abstract

Merapi, an andesitic volcanic complex in Central Java, is one of the most frequently erupting volcanoes in Indonesia and poses a permanent threat to the surrounding population of over 1 million people. With frequently recurring volcanic activity, the sixty or so reported eruptions since the mid-1500s have caused ~7,000 fatalities and destroyed numerous villages in the region. In June 2006, an eruption affected the densely populated area on the volcano’s southern and south-eastern flanks for the first time in almost a century. The resultant block-and-ash flows (BAFs) travelled down an incised river valley (Kali Gendol) to a distance of 7 km from the source, breaking out of the main channel at four main locations. Unconfined (overbank) BAFs were generated, which covered the interfluve regions on either side of the main valley and buried buildings and other infrastructure features in the village of Kaliadem, situated on the western bank of the Gendol valley ~5 km from the summit of Merapi. Using traditional volcanological field-based methods and non-invasive, high-resolution ground-penetrating radar techniques, the morphology and internal architecture of these overbank deposits were studied in detail in order to evaluate the destructive impact of these flows in a local context. The results show that complex, local-scale variations in flow dynamics and deposit architectures are apparent and that BAFs are capable of transporting significant numbers of large blocks (>1–2 m) out of the valley confines. We propose a conceptual model for the escape of these channelised BAFs onto the interfluvial terrace at Kaliadem and show, through a stratigraphic analysis of the pyroclastic successions underlying the village and adjacent areas on the volcano’s southern flank, that the area has been affected repeatedly by overbank BAFs and explosive eruptions over the past few 100 years (and more).

Item Type:	Article
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Pure Connector
Date Deposited:	02 Feb 2015 17:02
Last Modified:	10 Aug 2023 15:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/51765
DOI:	10.1007/s11069-011-0044-x

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