Publications des scientifiques de l'IRD

Bernard B., Vries de B. V., Barba D., Leyrit H., Robin Claude, Alcaraz S., Samaniego Pablo. (2008). The Chimborazo sector collapse and debris avalanche : deposit characteristics as evidence of emplacement mechanisms. Journal of Volcanology and Geothermal Research, 176 (1 Special Issue), p. 36-43. ISSN 0377-0273.

Titre du document
The Chimborazo sector collapse and debris avalanche : deposit characteristics as evidence of emplacement mechanisms
Année de publication
2008
Type de document
Article référencé dans le Web of Science WOS:000260361100006
Auteurs
Bernard B., Vries de B. V., Barba D., Leyrit H., Robin Claude, Alcaraz S., Samaniego Pablo
Source
Journal of Volcanology and Geothermal Research, 2008, 176 (1 Special Issue), p. 36-43 ISSN 0377-0273
Chimborazo is a Late Pleistocene to Holocene stratovolcano located at the southwest end of the main Ecuadorian volcanic arc. It experienced a large sector collapse and debris avalanche (DA) of the initial edifice (CH-1). This left a 4 km wide scar, removing 8.0 +/- 0.5 km(3) of the edifice. The debris avalanche deposit (DAD) is abundantly exposed throughout the Riobamba Basin to the Rio Chambo, more than 35 km southeast of the volcano. The DAD averages a thickness of 40 m, covers about 280 km(2), and has a volume of >11 km(3). Two main DAD facies are recognized: block and mixed facies. The block facies is derived predominantly from edifice lava and forms >80 vol.% of the DAD, with a probable volume increase of 15-25 vol.%. The mixed facies was essentially created by mixing brecciated edifice rock with substratum and is found mainly in distal and marginal areas. The DAD has clear surface ridges and hummocks, and internal structures such as jigsaw cracks, injections, and shear-zone features are widespread. Structures such as stretched blocks along the base contact indicate high basal shear. Substratum incorporation is directly observed at the base and is inferred from the presence of substratum-derived material in the DAD body. Based on the facies and structural interpretation, we propose an emplacement model of a lava-rich avalanche strongly cataclased before and/or during failure initiation. The flow mobilises and incorporates significant substrata (10-14 vol.%) while developing a fine lubricating basal layer. The substrata-dominated mixed facies is transported to the DAD interior and top in dykes invading previously-formed fractures.
Plan de classement
Géophysique interne [066]
Localisation
Fonds IRD [F A010072643]
Identifiant IRD
fdi:010044094
Contact