Central vs flank eruptions at Teide-Pico Viejo twin stratovolcanoes (Tenerife, Canary Islands)

Teide-Pico Viejo stratovolcanoes, on the island of Tenerife (Canary Islands), have undergone several flank and central vent, lava flow and explosive phonolitic eruptions during the last 35 ka, without any apparent structural or petrological control on such a random location of eruption foci. The morphology and size of the volcanic edifices have been changing during that period, but this seems to have not affected the location of new eruptions. In order to investigate what determines the occurrence of either central or flank eruptions at Teide-Pico Viejo stratovolcanoes, we have performed several numerical experiments considering a wide range of situations in which the main physical conditions (topography, size, depth and shape of the magma chambers, presence of deviatoric stresses, internal structure) of the volcanic system have been changed. The results obtained show that the main control on the pathway that magma will follow to leave the chamber and reach the surface is exerted by the stress field distribution around the chamber, which is a function of the shape of the chamber. This suggests that in the case of Teide-Pico Viejo, where there is not a preferential location for new vents, each new phonolitic eruption is preceded by the modification of the existing magma chamber (or the emplacement of a new batch of magma) that does not necessarily matches the structure of the previous one. The presence of multiple shallow reservoirs containing eruptible magma also influences the stresses distribution around the erupting magma chamber. The numerical results also show that the existence of an extensional stress field plays a significant role in determining the position of the phonolitic feeder dykes. (C) 2008 Elsevier B.V. All rights reserved.