IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

3P2_2G-O24

Room B2

Date/Time: July 23 18:00-18:15

Diffusive Helium Emissions as a Precursory Sign of Volcanic Unrest at El Hierro Island,
Canary Islands, Spain
Eleazar Padron1 , Nemesio M Perez1 , Pedro A Hernandez1 , Hirochika Sumino3 , Gladys Melian1 , Jose
Barrancos1 , Dacil Nolasco1 , German Padilla1 , Samara Dionis2 , Fatima Rodriguez2 , Inigo Hernandez2 ,David Calvo2 , Keisuke Nagao3
1Environmental Research Division, ITER, Spain, 2 Instituto VolcanolÃşgico de Canarias, Spain,3
Geochemical Research Center, University of Tokyo, Tokyo, Japan
E-mail: eleazar@iter.esSince July 16, 2011, an anomalous seismicity at El Hierro island, the youngest and smallest of the Canary Islands,
was recorded by IGN seismic network. After the occurrence of more than 10,000 seismic events, a submarine
eruption took place 2 km off the southern coast of El Hierro Island on October 12, 2011. Frequent episodes ofturbulent gas emission and foaming, and the appearance of steamy lava fragments were observed on the sea
surface. As part of the volcanic surveillance of the island, the Instituto Volcanologico de Canarias (INVOLCAN)
geochemical monitoring program is carrying out diffuse helium surveys on the surface environment of El Hierro (soilatmosphere). This nobel gas has been investigated because it has been considered an almost ideal geochemicalindicator because it is chemically inert, physically stable, nonbiogenic, sparingly soluble in water under ambientconditions and almost non-adsorbable. The helium concentration gradients with respect to its value on air measured
at 600 sampling sites allow us to estimate a pure diffusive emission rate of helium throughout the island. Since thebeginning of the volcano-seismic unrest, 19 helium emission surveys have been carried out. The helium emission
rate has shown an excellent agreement with the evolution of the volcanic crisis of the island, reaching 30 kg/d on
October 6, several days before the occurrence of the submarine eruption. A significant decrease to 13 kg/d wasestimated almost 10 days after the beginning of the eruption, followed by a sudden increase to 38 kg/d several
days before the largest seismic event of the volcanic crisis (M = 4.6) occurred on November 11. On 5 March, thesubmarine eruption was over, but the volcanic process that started in mid-July 2011 had not finished. By the end ofJune 2012, a new seismic unrest episode occurred, accompanied by the highest deformation rate measured in theisland during the unrest period. Within this phase, a new increase on the diffusive helium emission (up to 20 kg/d)
was observed.
Helium emission data measured in El Hierro 2011-2012 volcano-seismic unrest demonstrate that diffuse helium
surveys is a powerful tool for volcano monitoring. The geochemical parameters presented here are extremely
important for forecasting the onset of volcanic unrest and subsequent volcanic eruptions, mainly when magma
migrates aseismically, i.e., silently, toward the surface.

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