Report on Hierro (Spain) — 22 February-28 February 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 22 February-28 February 2012
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2012. Report on Hierro (Spain). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 22 February-28 February 2012. Smithsonian Institution and US Geological Survey.
27.73°N, 18.03°W; summit elev. 1500 m
All times are local (unless otherwise noted)
Instituto Geográfico Nacional (IGN) reported that during 22-28 February the seismic amplitude recorded at every IGN station on El Hierro Island remained at very low values. Weak and intermittent discoloration was observed on the sea surface over the emission area. Only once were emitted lava fragments observed during the reported period.
One-hundred and seven seismic events were located, most of them in the central part of the island, with a few extending offshore to the S. Depths of the hypocenters varied between 8 and 20 km and magnitudes between 0.1 and 2.6 (46 events with magnitude 1 or greater). Three events were felt by residents with a maximum intensity value of III (EMS-98). GPS deformation analyses showed a slight trend to N in the stations located at the N of the island.
Geologic Background. The triangular island of Hierro is the SW-most and least studied of the Canary Islands. The massive shield volcano is truncated by a large NW-facing escarpment formed as a result of gravitational collapse of El Golfo volcano about 130,000 years ago. The steep-sided scarp towers above a low lava platform bordering 12-km-wide El Golfo Bay, and three other large submarine landslide deposits occur to the SW and SE. Three prominent rifts oriented NW, NE, and S form prominent topographic ridges. The subaerial portion of the volcano consists of flat-lying Quaternary basaltic and trachybasaltic lava flows and tuffs capped by numerous young cinder cones and lava flows. Holocene cones and flows are found both on the outer flanks and in the El Golfo depression. Hierro contains the greatest concentration of young vents in the Canary Islands. Uncertainty surrounds the report of an eruption in 1793. A submarine eruption took place about 2 km SSW off the southern point of the island during 2011-12.