Spatial and temporal variations of diffuse CO₂ degassing at El Hierro volcanic system: Relation to the 2011–2012 submarine eruption

Abstract

We report herein the results of extensive diffuse CO 2 emission surveys performed on El Hierro Island in the period 1998-2012. More than 17,000 measurements of the diffuse CO 2 efflux were carried out, most of them during the volcanic unrest period that started in July 2011. Two significant precursory signals based on geochemical and geodetical studies suggest that a magma intrusion processes might have started before 2011 in El Hierro Island. During the preeruptive and eruptive periods, the time series of the diffuse CO 2 emission released by the whole island experienced two significant increases. The first started almost 2 weeks before the onset of the submarine eruption, reflecting a clear geochemical anomaly in CO 2 emission, most likely due to increasing release of deep-seated magmatic gases to the surface. The second one, between 24 October and 27 November 2011, started before the most energetic seismic events of the volcanic-seismic unrest. The data presented here demonstrate that combined continuous monitoring studies and discrete surveys of diffuse CO 2 emission provide important information to optimize the early warning system in volcano monitoring programs and to monitor the evolution of an ongoing volcanic eruption, even though it is a submarine eruption.

Insights into the 2011-2012 submarine eruption off the coast of El Hierro (Canary Islands, Spain) from statistical analyses of earthquake activity

“…From October 15 onwards, a sharp increase of the total CO 2 output occurred, peaking, on November 27, at 2.143 t·d −1 . This maximum was followed by a gradual decrease until the present (Melián et al 2012). Helium emission also showed a peak in early November (Padrón et al 2012), just few days before the largest seismic event in the sequence ( M l = 4.6).…”

Magma storage and migration associated with the 2011–2012 El Hierro eruption: Implications for crustal magmatic systems at oceanic island volcanoes

“…The collapse of an ~25 km deep magma reservoir could favor a transient increase in magma ascent rate. Evidence for a new, less‐degassed (more primitive) magma batch is supported by the significant increment of CO 2 soil diffuse efflux surveys in November‐December 2011 [ Melián et al ., ].…”

Evidence from acoustic imaging for submarine volcanic activity in 2012 off the west coast of El Hierro (Canary Islands, Spain)

“…2b). This submarine volcanic eruption was preceded by (i) an unusual increase of seismicity (more than 9000 seismic events) recorded by the National Geographical Institute of Spain (IGN) since July 19, 2011, (ii) a significant ground deformation detected by the seven-GPS network (Nagoya University-ITER-GRAFCAN) deployed at El Hierro (Sagiya et al 2012), and (iii) by significant changes in the volcanic gas emissions, detected both by the continuous geochemical monitoring network Padilla et al 2013) and by discrete geochemical surveys of diffusive helium emission and 3 He/ 4 He ratio data of dissolved gases in groundwater ) and diffuse CO 2 emissions (Melián et al 2014). From the starts of the submarine eruption, a large area of discolored water in the sea was observed most of the time, from light green to dark brown color, caused by chemical interaction of seawater with the intensely discharging of high-temperature volcanic hydrothermal fluids plus magmatic gases.…”