Large Earthquake near Jan Mayen Island.

On Thursday 30 August, slightly before 1.45 pm local time (which is the same as GMT), the United States Geological Survey recorded an Earthquake measuring 6.8 on the Richter Scale at a depth of 9.9 km, on the Mid-Atlantic Ridge, roughly 400 km east of Greenland. This is a large Earthquake and could cause considerable problems in an inhabited area, though it is unlikely to have done so in the remote North Atlantic, where the only inhabited place likely to have felt shaking would be Jan Mayen Island, 100 km southeast of the quake's center, where the Norwegian Armed Forces and the Norwegian Meteorological Institute both maintain bases, the island's population occasionally rising as high as 35. This quake was followed after about eight minutes by another quake roughly 5 km southeast of Jan Mayen, this time measuring 5.2 on the Richter Scale, at a depth of 12.3 km.

Map showing the locations of the first (A) and second (B) quakes on 30 August 2012. Google Maps.

The Mid-Atlantic Ridge is a divergent plate margin running the length of the Atlantic from north to south, and separating North and South America to the west from Eurasia and Africa to the east. The Atlantic is spreading at an average rate of 25 mm per year, with new seafloor being produced along the rift volcanically, i.e. by basaltic magma erupting from below. In places this produces volcanic activity above the waves, in the Azores, on Iceland and on Jan Mayen Island itself, where the Beerenberg Volcano is the most northerly active volcano on the planet.

See also Earthquake in the Azores, Magnitude 6.2 Earthquake north of Norway, The dangers of a modern Laki style eruption in Iceland, The Hekla Volcano - is the Gateway to Hell about to open? and Earthquakes on Sciency Thoughts YouTube.

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Is Mount Cleveland, Alaska, about to erupt?

On Wednesday the 20th July 2011 the Alaska Volcano Observatory issued an advisory warning on Cleveland Volcano in the Aleutian Islands, following the detection of thermal anomalies in satellite data. Since then the weather has prevented further satellite observations, and the warning remains in place.

Cleveland is located on the uninhabited Chuginadak Island, 1500 km southwest of Anchorage, and 75 km from the nearest settlement, Nikolski on Umnak Island, a village of 39 people. Due to its remote location it it seldom visited, and does not merit a network of seismometers, so there is not data available other than that from satellites.

Cleveland Volcano, in a remote part of the Aleutian Islands.

Cleveland has a history of sudden, explosive eruptions, it's last major eruption, in February 2001, threw ash 12 km into the air and produced a lava flow that reached the sea, so it is considered a hazard to aircraft.

Cleveland is a stratovolcano, a volcano formed by layers of ash and lava deposits with a classic cone shape. It rises 1730 m above the sea level, and is about 8 km across at the base. It shows little sign of erosion, and is probably no more than 10 000 years old. Due to its location it is completely treeless, and has little vegetation of any sort on its flanks, making its shape particularly notable.

An arial photograph of Mount Cleveland.

The Aleutians are a volcanic island arc, formed where the Pacific Plate is being subducted beneath the North American Plate; the arc actually continues onto land as the Aleutian Range, a string of volcanic mountains on the Alaskan Peninsula. As the Pacific Plate sinks into the Earth it is heated and partially melted; lighter minerals then rise up through the overlying North American Plate, forming volcanoes.

How volcanoes are formed by oceanic plate subduction.

See also Recent Eruptions on Mount Etna, New Submarine Volcanoes found in the South Sandwich Islands, and Volcanoes on Sciency Thoughts YouTube.

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