IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

1A1_3G-O4

Room A4

Date/Time: July 21 9:45-10:00

The control of source processes and topography on the dynamics of devastating
pyroclastic density currents generated during the Merapi 2010 eruption
Jean-Christophe Komorowski1 , Susanna Jenkins2 , Peter Baxter3 , Sylvain Charbonnier4 , Ralf
Gertisser5 , Katie Preece6 , Franck Lavigne7 , Noer Cholik8 , Surono Surono91Institut de Physique du Globe de Paris, 1 rue Jussieu 75238 Paris Cedex 05, France, 2 University ofBristol, Wills Memorial Building, Queen’s Road, Bristol, BS8 1RJ, UK, 3 Institute of Public Health,
University of Cambridge, Cambridge, CB2 2SR, UK, 4 Department of Geology, University of South
Florida, Tampa, 33620, FL, USA, 5 Keele University, Keele, ST55BG, UK, 6 School of Environmental
Sciences, University of East Anglia, Norwich NR4 7TJ„ UK, 7 UniversitÃl’ Paris 1 Pantheon Sorbonne,
CNRS UMR 8591, France, 8 BPPTK Yogyakarta, 55166, Indonesia, 9 CVGHM Jalan Diponegoro 57,40122 Bandung, Indonesia
E-mail: komorow@ipgp.fr

The Merapi 2010 eruption, the most intense at Merapi since 1872, provided a unique detailed empirical dataset on
the generation, emplacement, and devastating impact of a diversity of pyroclastic density currents (PDCs) during
an escalating rapid-onset, multi-stage eruption that threatened a large population. An 11-minute sequence oflaterally-directed explosions and retrogressive collapses on 5 November 2010 at Merapi destroyed a rapidly-growing
dome and generated high-energy PDCs (stage 4) spreading over 22 km2 with a runout of 8.4 km, while co-genetic
valley-confined PDCs reached 15.5 km. The deposits and the widespread devastating impact of associatedhigh-energy PDCs on trees and buildings show striking similarities with those from historical volcanic blasts(Montagne Pelee, Bezymianny, Mount St. Helens, Soufriere Hills). We provide data from extensive stratigraphic
and sedimentologic field studies of the first unequivocal blast-like deposits in the recent history of Merapi. We
used high resolution satellite imagery to map eruptive units and flow direction from the pattern of extensive tree
blowdown. The stratigraphy of Stage 4 PDCs consists of three depositional units (U0, U1, U2) that we correlate withthe second, third and fourth explosions of the seismic record. Both U1 and U2 show a bi-partite layer stratigraphyeach with a lower L1 layer and an upper L2 layer. The lower L1 layer is typically very coarse-grained, fines-poor,poorly-sorted and massive, and was deposited by the erosive waxing flow head. The overlying L2 layer is muchfiner grained, fines-rich, moderately to well-sorted, with laminar to wavy stratification. L2 was deposited from thewaning upper part and wake of the PDC. Field observations indicate that PDC height reached 330 m with aninternal velocity of 100 m.s-1 within 3 km from the source. The geometry of the summit and terrain morphology
formed by a major transversal ridge and a funneling deep canyon significantly limited the loss of kinetic energyof the PDC hence focussing their mass into a major canyon constriction. The resulting elevated PDC velocities
and high particle concentration promoted overspilling of high ridges into tributary valleys, while generating elevateddynamic pressures offset from the crater that caused major destruction of buildings and forest to 6 km from thesummit. The Merapi 2010 eruption highlights that source and path effects can significantly control the dynamics ofhigh-energy PDCs generated as a result of explosive and gravitational disintegration of a rapidly growing dome. This
constitutes a challenge for current efforts in mathematical modelling of PDCs and quantitative risk assessment ofpotential impact areas at Merapi and at other volcanoes, particularly during multi-stage eruptions that can generate
a diversity of PDCs in a short time-period during which the properties of the substratum over which succesive PDCs
are emplaced can evolve significantly with time.

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