A LARGE VOLCANIC DEBRIS AVALANCHE IN THE PLIOCENE ROQUE-NUBLO STRATOVOLCANO, GRAN-CANARIA, CANARY-ISLANDS

Citation
Lg. Cacho et al., A LARGE VOLCANIC DEBRIS AVALANCHE IN THE PLIOCENE ROQUE-NUBLO STRATOVOLCANO, GRAN-CANARIA, CANARY-ISLANDS, Journal of volcanology and geothermal research, 63(3-4), 1994, pp. 217-229
Citations number
31
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geology
ISSN journal
0377-0273
Volume
63
Issue
3-4
Year of publication
1994
Pages
217 - 229
Database
ISI
SICI code
0377-0273(1994)63:3-4<217:ALVDAI>2.0.ZU;2-5
Abstract
During the second magmatic cycle of Gran Canaria, between 5 and 3 Ma, the Roque Nublo Stratovolcano (RNS) achieved its almost total developm ent, reaching a height of 2500-2600 m and spreading about 100 km3 of p roducts over a surface area of at least 250 km2. In the last growth st age of the RNS, and probably in connection with the paroxysmic genesis of the Roque Nublo explosive Caldera, a sector of the volcanic edific e suffered a gravitational collapse of significant importance. The dat a reported here show that the collapse was accompanied by a great aval anche: the Roque Nublo Debris Avalanche Deposit (RNDAD) composed mainl y of block facies. The last explosive emissions of the RNS were restri cted to ignimbrites and some explosive breccias that locally overlap t he avalanche deposits. The features of the outcrops along the course o f the avalanche make it possible to distinguish between the proximal, intermediate and distal deposits. The debris avalanche (3-4 km3) moved SW then S, and finally SSE. Part of the deposit, mainly formed by lar ge megablocks, remained very near the source area. Halfway along the c ourse, the avalanche was channelled by broad and steep paleovalleys. I n the most distal areas, the RNDAD opens into a fan-shape, reaching a distance of 28-30 km. A simplified kinematical physical model is used to understand the movement of the RNDAD. The model is based on the spe culative reconstruction of the RNS edifice, based in turn on its scarc e peripheral remains. An arbitrary avalanche path was selected, with a total travel distance from the source area (top of the stratovolcano) of 28 km. With these assumptions it is possible to calculate the spee d at each point (V(m) = 90 m/s) and other parameters that show that th e RNDAD is very similar to other well-known volcanic avalanches.