Abstract
Abstract During the second magmatic cycle of Gran Canaria, between 5 and 3 Ma, the Roque Nublo Stratovolcano (RNS) achieved its almost total development, reaching a height of 2500–2600 m and spreading about 100 km 3 of products over a surface area of at least 250 km 2 . In the last growth stage of the RNS, and probably in connection with the paroxysmic genesis of the Roque Nublo explosive Caldera, a sector of the volcanic edifice suffered a gravitational collapse of significant importance. The data reported here show that the collapse was accompanied by a great avalanche: the Roque Nublo Debris Avalanche Deposit (RNDAD) composed mainly of block facies. The last explosive emissions of the RNS were restricted to ignimbrites and some explosive breccias that locally overlap the avalanche deposits. The features of the outcrops along the course of the avalanche make it possible to distinguish between the proximal, intermediate and distal deposits. The debris avalanche (3–4 km 3 ) moved SW then S, and finally SSE. Part of the deposit, mainly formed by large megablocks, remained very near the source area. Halfway along the course, the avalanche was channelled by broad and steep paleovalleys. In 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 speculative reconstruction of the RNS edifice, based in turn on its scarce 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 speed at each point ( V m = 90 m/s) and other parameters that show that the RNDAD is very similar to other well-known volcanic avalanches.
Published Version
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