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Friday, October 21, 2011

World Volcanic Activity Report – Katla, El Hierro, Tambora, Shiveluch

The Weekly Volcanic Activity Report, a cooperative project between the Smithsonian’s Global Volcanism Program and the US Geological Survey’s Volcano Hazards Program, covers the period 12-19 October, 2011.

This week’s update features information on the ongoing volcanic activity at the Puyehue-Cordón Caulle volcanic complex in Chile and the increase in seismic activity at the Katla volcano in southern Iceland.

Other active volcanoes featured this week include El Hierro in the Canary Islands (Spain), Marapi and Tambora in Indonesia, Fuego in Guatemala, Sakura-Jima in Japan, Shiveluch and Kizimen in Russia, Manam in New Guinea, and Mount Cleveland and Kilauea in the United States (U.S.A.).

This information page is broken into two categories, namely “New Activity/Unrest” and “Ongoing Activity”.
New Activity/Unrest

HIERRO Canary Islands (Spain) 27.73°N, 18.03°W; summit elev. 1500 m

MODIS image of El Hierro on the afternoon of Friday 14 October 2011

Instituto Geográfico Nacional (IGN) reported that tremor, registered by every seismic station on El Hierro Island, continued during 12-18 October. Deformation decreased during this period, with significant inflation-deflation episodes registered by the stations located in the NW part of the island. On 12 October, at about 1430, the amplitude of the tremor signals abruptly decreased and smaller amplitudes persisted during the following days. During the afternoon of 12 October a large light-green colored area was observed in the sea to the S of La Restinga village (at the southernmost point of Hierro); the evolution of this anomaly was observed from land and by helicopter. The extension of the anomaly was controlled by the ocean currents, but a small area was detected as the emission center due to its intense discoloration and concentration.

During a helicopter flight on 15 October, steamy lava fragments in this small area were observed. In the same area, during 15-17 October, frequent episodes of emission, forming big turbulent rings of gas and foaming, were observed on the sea surface. Since the night of 17 October, the amplitude of the tremor signal had decreased slowly. On 18 October, deformation further decreased and the sea-surface disruption from gases was not observed.

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.