Unrest signals after 46 years of quiescence at Cumbre Vieja, La Palma, Canary Islands
Monogenetic eruptions are the most common volcanic activity in the world. However, unrest monitoring data are scarce due to the long intervening quiescence periods. This study analyzes unrest signals recorded in one of the largest monogenetic fields in the Canary Islands, Cumbre Vieja (La Palma). Two seismic swarms were registered in October 2017 and February 2018 with b-values of 1.6 ± 0.1 and 2.3 ± 0.2 respectively suggesting an intense magmatic fluids contribution, gas and/or magma. Both swarms were linked to changes in gas emissions. Increases in hydrogen concentration, and (R/Ra)c up to 7.52±0.05, were recorded before the first swarm, at the sampling point closest to where seismicity was located, indicating a deep gas input. After the second swarm, increases in (R/Ra)c and thoron soil concentration were recorded at two locations. This dataset is compatible with a stalled magmatic intrusion at ca. 25 km depth, with an estimated volume between 5.5·10−4 km3 and 3·10−2 km3.
Hydrothermal system of Central Tenerife Volcanic Complex, Canary Islands (Spain), inferred from self-potential measurements.
An extensive self-potential survey was carried out in the central volcanic complex of Tenerife Island (Canary Islands, Spain). A total amount of ~237 kmof profileswith 20 mspacing betweenmeasurementswas completed, including radial profiles extending from the summits of Teide and Pico Viejo, and circular profiles inside and around Las Cañadas caldera and the northern slopes of Teide and Pico Viejo. One of themain results of this mapping is the detection ofwell-developed hydrothermal systemswithin the edifices of Teide and Pico Viejo, and also associated with the flank satellite M. Blanca and M. Rajada volcanoes. A strong structural control of the surface manifestation of these hydrothermal systems is deduced from the data, pointing to the subdivision of Teide and Pico Viejo hydrothermal systems in three zones: summit crater, upper and lower hydrothermal systems. Self-potential maxima related to hydrothermal activity are absent from the proximal parts of the NE and NW rift zones as well as from at least two of the mafic historical eruptions (Chinyero and Siete Fuentes), indicating that long-lived hydrothermal systems have developed exclusively over relatively shallow felsic magma reservoirs. Towards Las Cañadas caldera floor and walls, the influence of the central hydrothermal systems disappears and the self-potential signal is controlled by the topography, the distance to thewater table of Las Cañadas aquifer and its geometry. Nevertheless, fossil or remanent hydrothermal activity at some points along the Caldera wall, especially around the Roques de García area, is also suggested by the data. Self-potential data indicate the existence of independent groundwater systems in the three calderas of Ucanca, Guajara and Diego Hernández, with a funnel shaped negative anomaly in the Diego Hernández caldera floor related to the subsurface topography of the caldera bottom. Two other important self-potential features are detected: positive values towards the northwestern Santiago rift, possibly due to the relatively high altitude of the water-table in this area; and a linear set ofminima to thewest of Pico Viejo, aligned with the northwestern rift and related to meteoricwater infiltration along its fracture system.
Xenopumices from the 2011–2012 submarine eruption of El Hierro (Canary Islands, Spain): Constraints on the plumbing system and magma ascent
Textures, petrography and geochemical compositions of products emitted during the onset of the 2011–2012 submarine eruption (15 October, 2011) off the coast of El Hierro have been investigated to get information on interaction mechanism between the first rising magma and the crust during the onset of the eruption as well as to get information on magma storage and plumbing systems beneath El Hierro volcano. Studied products consist of 5–50 cm bombs with an outer black to greenish, vesicular crust with bulk basanite composition containing pumiceous xenoliths (xenopumices). Our results show that xenopumices are much more heterogeneous that previously observed, since consist of a macro-scale mingling of a gray trachyte and white rhyolite. We interpreted xenopumices as resulting from the interaction (heating) between the basanitic magma feeding the eruption, a stagnant trachytic magma pocket/s and an associated hydrothermally altered halo with rhyolitic composition. Our findings confirm the importance of the study of the early products of an eruption since they can contain crucial information on the plumbing system geometry and the mechanism of magma ascent.