Report on Hierro (Spain) — 4 July-10 July 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 4 July-10 July 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, 4 July-10 July 2012. Smithsonian Institution and US Geological Survey.
27.73°N, 18.03°W; summit elev. 1500 m
All times are local (unless otherwise noted)
On 11 July Instituto Geográfico Nacional (IGN) reported that seismic activity and deformation at Hierro had decreased since the previous week. During 4-10 July there were 650 seismic events located, most of them offshore SW of El Hierro Island at 20 km depth. The maximum magnitude recorded was 3.8, which occurred on 10 July at 0504, and 77 earthquakes were M 2.7 or higher. The total number of located events had reached more than 2,200 since the anomalous activity began on 24 June. The deformation during this period had maximum values of about 1.5 cm in the horizontal component and 1.5 cm of vertical displacement.
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.