Internal structure of the western flank of the Cumbre Vieja volcano, La Palma, Canary Islands, from land magnetotelluric imaging

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) to map the structures underneath and (3) to 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 off ridge, along the western flank in an en echelon fashion.

Three‐dimensional resistivity structure and magma plumbing system of the Kirishima Volcanoes as inferred from broadband magnetotelluric data

“…The black dashed circle indicates the possible location of the source of deformation Nakao et al, 2013;Kozono et al, 2013]. Hydrothermally altered minerals (especially smectite) show a significantly low resistivity, and this has been considered an important cause of the low resistivity within active volcanoes [e.g., Jones and Dumas, 1993;Ogawa et al, 1998;Nurhasan et al, 2006;Coppo et al, 2008;Aizawa et al, 2009a;Yamaya et al, 2009;Garcia and Jones, 2010;Kanda et al, 2010;Siniscalchi et al, 2012]. By taking into account bore data at Ogiri geothermal field [Uchida and Sasaki, 2006], the widespread, shallow (a few kilometers deep) conductors are interpreted as a zone of hydrothermal alteration whose base corresponds to the 200°C isotherm.…”

Flank instability structure of Mt. Etna inferred by a magnetotelluric survey

“…Although MT has not often been used at Etna, a wealth of literature bears witness to the effectiveness of this electromagnetic method for investigations of other volcanic areas [ Bartel and Jacobson , 1987; Descloitres et al , 1997; Aizawa et al , 2009a, 2009b; Hill et al , 2009; Garcia and Jones , 2010; Ingham et al , 2009]. MT can provide information on structural contrast, fluids, and partial melts at depths ranging from hundreds of meters to tens of kilometers.…”

Surface geochemical and geophysical studies for geothermal exploration at the southern volcanic rift zone of Tenerife, Canary Islands, Spain

“…This alteration layer is expected to have a very low permeability, so any gap in this layer could be related with surface manifestations of gases. Magnetotelluric surveys have been used in volcanic areas for structural investigation, geothermal evaluation and hydrothermal circulation (García and Jones, 2010;Heise et al, 2008;Ingham et al, 2009;Uchida and Sasaki, 2006). Five MT surveys have been performed in Tenerife (Coppo et al, 2008(Coppo et al, , 2010Ortiz et al, 1986;Piña-Varas et al, 2014;Pous et al, 2002).…”