HIERRO Canary Islands (Spain) 27.73°N, 18.03°W; summit elev. 1500 m
Instituto Geográfico Nacional (IGN) reported more than 700 new seismic events were detected at Hierro during 4-11 October, 52 of them were felt by residents. A M 4.3 earthquake was detected on 8 October, located 1.5 km from the SW coast of the island at 14 km depth. Following the event, the trend of the superficial deformation changed, suggesting deflation of the system. During the night of 8 October through the following day, low-magnitude seismic events occurred at depths of less than 2 km. Since 0515 on 10 October volcanic tremor was clearly recorded by all of the seismic stations on the island, with highest amplitudes recorded in the southernmost station. All data suggested a submarine eruption.
On 11 October at about 0700 the amplitude of the tremor increased. During that morning residents on the S of the island reported feeling vibrations. After midday, the Government of the Canary Islands raised the Alert Code to Red for Restinga village (at the southernmost point of Hierro) and evacuated the residents. A maritime exclusion zone extended about 4 nautical miles from Restinga.
Geologic Summary. The triangular island of Hierro is the SW-most and least studied of the Canary Islands. The massive Hierro 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 1500-m-high 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.
October 13, 2011 – CANARY ISLANDS – These are some of the first images of the sea surface off the coast of La Restinga, near El Hierro. Residents of El Hierro have been observing the formation of ‘green patches’ on the sea surface, some 1 and a half miles from land, which appears to be growing in size at a rapid pace since this morning. There is also a strong smell of sulfur in the air and reports of schools of dead fish have been found near the eruption site. In the meantime, tremors continue on the island of El Hierro. Though tremor intensity has quelled- volcanic activity continues bubbling under the island and ocean. This could perhaps be volcanic fissures that erupted in the ocean along the pathway to vent some of the magma and gases that are rumbling under the island. It may be only a small leak in the pipe and nothing more. Magma plumes are large unpredictable volcanic features that punch holes in the earth’s crust as tectonic plates are jostled over them. It remains to be seen what develops next from all this seismic activity. In the ocean- such magma plumes create islands. According to reports in the Canaries News, (source of the Twitter feed) the specialists and researchers working from the La Restinga area of El Hierro have confirmed that there is clear evidence of two underwater eruptions which have pushed magma up to the surface of the water.
Although the earth directed surface has a large number of sunspots, and some with significant magnetic complexity, activity has remained low to moderate with a 35% chance of an M-Class flare.
NEW WATCH ITEM -Seattle and NW Area.
Two earthquakes have been recorded on 10-15. A 2.5 dead center in the cone. The National Volcano Center has NOT raised watch level from green, but we would say it is green-yellow at this point. If we start to see swarming, then we go yellow.