Nuées ardentes of 22 November 1994 at Merapi volcano, Java, Indonesia.

E.K. Abdurachman (1, 2) , Jean-Louis Bourdier (3, 4) , B. Voight (5)

1 Volcanological Survey of Indonesia
2 Géotectonique, géophysique, métallogénie
3 ISTO - Institut des Sciences de la Terre d'Orléans
4 Centre de Recherches Volcanologiques
5 University of Pennsylvania

Nuées ardentes associated with dome collapse on 22 November 1994, at Merapi volcano traveled to the south-southwest as far as 6.5 km, and collectively accumulated roughly 2.5-3 million cubic meters of deposits. The damaged area comprises 9.5 km2 and is covered by two nuée ardente facies, a conventional "Merapi-type", valley-fill block-and-ash flow facies and a pyroclastic surge facies. The proximal deposits reflect the accumulation of dozens of nuées ardentes, with many subsidiary flow units. The distal deposits are more simply organized, as only a few individual events reached to distances >3.5 km. The stratigraphic relationships north of Turgo hill indicate that the surge deposits are a facies of particularly mobile nuées ardentes that also deposited channeled block-and-ash flow facies. They further suggest that the surge facies beyond the channel margins correlate laterally with a finer-grained sublayer locally developed at the base of the block-and-ash flow facies. Eyewitness reports suggest that the emplacement of the block-and-ash flow facies in the distal part of the Boyong river may have followed, by a short time interval, the destruction and deposition of the surge facies at Turgo village. The stratigraphy is in accord with the eyewitness reports. The surge facies was emplaced by a dilute surge current, detached from the same dome-collapse nuée ardente that, as a separate flow unit, subsequently emplaced the distal block-and-ash deposit in the Boyong valley. The detachment occurred at higher elevations, likely at or above the slope break at about 2000 m elevation. This flow separation enabled the surge current to shortcut over the landscape and to emplace its deposit even as the block-and-ash flow continued its tortuous southward movement in the Boyong channel. Dome-collapse nuée ardente activity formed the bulk of the eruption, which was accompanied by virtually no significant vertical summit explosive activity.

Mots clés: nuées ardentes; Merapi volcano; block-and-ash flow; pyroclastic range; lava dome

Domaines: Volcanologie; Milieux et Changements globaux

E.K. Abdurachman, Jean-Louis Bourdier, B. Voight. Nuées ardentes of 22 November 1994 at Merapi volcano, Java, Indonesia.. Journal of Volcanology and Geothermal Research, 2000, 100, pp.345-361. ⟨10.1016/S0377-0273(00)00144-X⟩. ⟨hal-00091175⟩