Report on Hierro (Spain) — 25 January-31 January 2012
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 25 January-31 January 2012
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2012. Report on Hierro (Spain) (Sennert, S, ed.). Weekly Volcanic Activity Report, 25 January-31 January 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 25-31 January the submarine eruption continued S of El Hierro Island. Mean tremor amplitude maintained very low values during this report period. Frequent and persistent emissions of large steaming lava fragments were observed on the sea surface, some of them about 3 m wide.
Seventy-eight seismic events were registered during this period, most of them located in the central part of the island, with offshore events extending primary to the S. Depths of the hypocenters varied between 10 and 23 km, and magnitudes between 0.4 and 2.8. Analyses of GPS deformation showed stability both in vertical and horizontal components.
Geological Summary. 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.