Monitoring the volcanic unrest of El Hierro (Canary Islands) before the onset of the 2011-2012 submarine eruption

El Hierro is, together with La Palma, the youngest island of the Canarian Archipelago. Both islands are in the shield stage of their volcanic growth, which implies a high volcanic activity during the Holocene period. The submarine eruption occurred in October 2011 in the SSE rift of El Hierro evidenced the active volcanic character of the island. Even so, despite the numerous scientific works published following the submarine eruption (most of them centered to understand such volcanic event), there is still a lack of precise knowledge about the Holocene subaerial volcanism of this island. The LAJIAL Project focuses on solving this knowledge gap.The Holocene subaerial volcanism of El Hierro generates fields of monogenetic volcanoes linked to the three systems of rifts present on the island. Its eruptive mechanisms are typically Strombolian although there are also phreato-Strombolian events. The most recent eruptions frequently form lava on coastal platforms, which are considered after the last glacial maximum (approx. 20 ka BP). The most developed coastal platforms in El Hierro are at the ends of the rifts and in the interior of the El Golfo depression. This geomorphological criterion shows that more than thirty subaerial eruptions have taken place in El Hierro since approx. 20 ka BP. In addition, there are many apparently recent volcanic edifices far from the coast.The research of the most recent volcanism of the island, the last 11,700 years of the Holocene, covers a long enough period whereas it is close to the present day. Thus, this period is the best to model the eruptive processes that will allow us to evaluate the future scenarios of the eruptive dynamics in El Hierro. The Project LAJIAL combines methodologies of geological mapping, geomorphology, GIS, chronostratigraphy, paleomagnetism, petrology and geochemistry to solve the Holocene eruptive recurrence rate in El Hierro, and to constrain the rift model of intraplate ocean volcanic islands.Financial support was provided by the Project LAJIAL (ref. PGC2018-101027-B-I00, MCIU/AEI/FEDER, EU). This study was carried out in the framework of the Research Consolidated Groups GEOVOL (Canary Islands Government, ULPGC) and GEOPAM (Generalitat de Catalunya, 2017 SGR 1494).

Download Full-text

Spatial-temporal variations of surface diffuse CO2 degassing at El Hierro volcano, Canary Islands

10.5194/egusphere-egu2020-11805 ◽

2020 ◽

Author(s):

Pedro A. Hernández ◽

Christopher A. Skeldon ◽

Jingwei Zhang ◽

Fátima Rodríguez ◽

Cecilia Amonte ◽

...

Keyword(s):

Canary Islands ◽

Temporal Variations ◽

Graphical Analysis ◽

Homogeneous Distribution ◽

Submarine Eruption ◽

El Hierro ◽

North East ◽

The North ◽

Total Data ◽

Destructive Processes

El Hierro (278 km2), the youngest, smallest and westernmost island of the Canarian archipelago, is a 5-km-high edifice constructed by rapid constructive and destructive processes in ~1.12 Ma, with a truncated trihedral shape and three convergent ridges of volcanic cones. It experienced a submarine eruption from 12 October, 2011 to 5 March 2012, off its southern coast that was the first one to be monitored from the beginning in the Canary Islands. As no visible emanations occur at the surface environment of El Hierro, diffuse degassing studies are a useful geochemical tool to monitor the volcanic activity in this volcanic island. Diffuse CO2 emission surveys have been performed at El Hierro Island since 1998 in a yearly basis, with much higher frequency during the period 2011-2012. At each survey, about 600 sampling sites are selected to obtain a homogeneous distribution. Measurements of soil CO2 efflux are performed in situ following the accumulation chamber method. During pre-eruptive and eruptive periods, the diffuse CO2 emission released by the whole island experienced significant increases before the onset of the submarine eruption and the most energetic seismic events of the volcanic-seismic unrest (Meli&#225;n et al., 2014. J. Geophys. Res. Solid Earth, 119, 6976&#8211;6991). The most recent diffuse CO2 efflux survey was carried out in July 2019. Values ranged from non-detectable to 28.9 g m&#8722;2 d&#8722;1. Statistical-graphical analysis of the data shows two different geochemical populations; Background (B) and Peak (P) represented by 97.5% and 0.5% of the total data, respectively, with geometric means of 1.2 and 23.6 g m&#8722;2 d&#8722;1, respectively. Most of the area showed B values while the P values were mainly observed at the interception center of the three convergent ridges and the north-east of the island. To estimate the diffuse CO2 emission for the 2019 survey, we ran about 100 sGs simulations. The estimated 2019 diffuse CO2 output released to atmosphere by El Hierro was 214 &#177; 10 t d-1, value lower than the background average of CO2 emission estimated on 412 t d-1 and slightly higher than the background range of 181 t d-1 (&#8722;1&#963;) and 930 t d-1 (+1&#963;) estimated at El Hierro volcano during the quiescence period 1998-2010 (Meli&#225;n et al., 2014, JGR). Monitoring the diffuse CO2 emission has proven to be a very effective tool to detect early warning signals of volcanic unrest at El Hierro.

Download Full-text