Publication 124
Internal structure of the western flank of the Cumbre Vieja volcano (La Palma, Canary Islands)
from land magnetotelluric imaging
Xavier Garcia and Alan G. Jones
Abstract
Large-scale mass wasting is a natural part of the evolution of
volcanic islands, where deformation and indications of flank instability, such
as large-scale faulting and seismic and aseismic slip are common. The Cumbre Vieja
volcano on the island of La Palma (Canary Islands) provides an
ideal setting to address fundamental questions about the structure, evolution
and stability of island volcanoes. The island of La Palma is still in a shield-building
stage, and it has been postulated that the western side of the island
lies over a pre-existing zone of weakness that can nucleate ruptures. We
undertook an audiomagnetotelluric (AMT) survey over the proposed unstable
western flank to try to image structures that may be associated with the
zone of weakness. The magnetotelluric method (MT) is a geophysical technique
used to map the presence of fluids or image important structural contrasts.
The goals of this study were (1) to delineate the unstable flank, (2)
map the structures underneath and (3) determine the presence and geometry
of fluids. The results show a 1 km thick top resistive layer overlaying
an area of reduced resistivity (enhanced conductivity), interpreted as a layer
consisting of an alteration zone and also fluids. Our results confirm previous
studies that suggested the existence of a western flank lying over collapse
debris material and hyaloclastites, and also they allow us to map part of the
subaerial southern extent of the Cumbre Nueva units that lie beneath the
more recent Cumbre Vieja rocks. In addition, dimensionality analysis maps
the rotation of the dike emplacement o� ridge, along the western flank in an
en echelon fashion.
Source
Journal of Geophysical Research - Solid Earth, 115, B07104, doi: 10.1029/2009JB006445, 2010.
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Alan G Jones / 03 AUGUST 2010 /
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