El Heirro had remained quiescent over the last 10 days with small offshore eruptions occurring. It seemed that these undersea eruptions had relieved much of the pressure and magma levels seemed to become stable. However, over the last 48 hours there seems to be new unrest and looking at the most recent seismic data (see below) indicates that the magma may be on the move again. While this is may NOT be indicative of an impending eruption, we have to move back into the “yellow” zone for watching this very potentially dangerous volcano. What concerns us the most, as noted by the data below, is the depth of the eruptions is rising again with the latest significant quake having risen to the 11 KM depth. East Coasters pay attention.
New Activity/Unrest – October 27th, 2011
HIERRO Canary Islands (Spain) 27.73°N, 18.03°W; summit elev. 1500 m
Instituto Geográfico Nacional (IGN) reported that during 19-25 October tremor continued to be registered by every seismic station on El Hierro Island; 270 seismic events were registered and located. The mean amplitude was lower than during previous days but indicated that the submarine eruption continued. Since 21 October, most of the events were located in the N part of the island, aligned NNW-SSE from the center of the island to around 13 km offshore. Most of these earthquakes occurred around 20-25 km depth. Superficial analysis of GPS deformation data from the last few days of the reporting period showed different behaviors between the stations located at the N of the island and the station located at the S, close to the submarine eruptive vent.
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.
2011-10-27 06:27 27.76 N 18.04 W 20 KM 3.1M CANARY ISLANDS, SPAIN REGION MAD
2011-10-27 12:38 27.79 N 18.06 W 19KM 2.6M CANARY ISLANDS, SPAIN REGION MAD
2011-10-27 17:26 27.64 N 18.02 W 11KM 2.8M CANARY ISLANDS, SPAIN REGION MAD