Report on Hierro (Spain) — 26 October-1 November 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 26 October-1 November 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Hierro (Spain). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 26 October-1 November 2011. 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 26 October-1 November tremor continued to be registered by every seismic station on El Hierro Island; 540 seismic events were registered and located, and the mean amplitude increased slightly during the last two days. Most of the events were located offshore to the N of the island, at depths of 16-23 km. The maximum magnitude was 3.9, and 36 of the total events were felt by residents at a maximum intensity value of IV using EMS-98 (European Macroseismic Scale). The total number of located events since 17 July was 10,930.
Preliminary analysis of GPS deformation data showed an inflation-deflation sequence at one station on the N side of the island, with the main deformation trending N-S and in vertical components. GPS stations located in the W and S showed different behavior, with mean deformations to the SW and NE, respectively.
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 south at 120 degree angles 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 historical eruption in 1793.