Friday 18 May 2012

Eruption on Mount Karthala.

Mount Karthala is the southernmost, and larger, of two shield volcanoes making up the island of Grand Comore (Ngazidja). Shield volcanos are broad, dome-shaped, volcanoes made up of successive layers of lava; shield volcanoes do not have the classic 'cone-shape' of stratovolcanoes, but can be far larger. Karthala reaches 2361 m above sea-level and has a central caldera 3 km by 4 km. It is an extremely active volcano, frequently producing lava-flows and ash-falls. Ash-falls from Karthala often cause water-contamination problems.

Map 0f Grande Comore showing the position on Karthala. Red line shows the limits of a proposed national park around the volcano. Ramsar.

On the night of 9-10 May 2012 residents of the villages of Mde and Mkazi, to the west of the volcano, reported seeing incandescence on the summit of Karthala, though there has been no reported activity since.

Karthala was last active between April 2005 and January 2007. This cycle started with a series of tremors on the morning of 16 April 2005, followed by the eruption of an ash column from the volcano in the afternoon, followed by ash-falls across the eastern side of the island. This continued into the next day causing local authorities to evacuate some eastern villages, then stopped abruptly during the next night; subsequent investigations on the summit revealed a substantial lava-lake had formed in the caldera.

On 24-25 November activity resumed on the volcano, with an ash-cloud spreading southeast of the summit, with ash-falls reaching the capitol, Moroni. The cloud reached 11 600 m in height, and the Toulouse Volcanic Ash Advisory Center issued an advisory limit to air-traffic. Again a number of villages were evacuated, and concern was raised about water contamination were raised. A large number of people reported respiratory problems, which were reported to have caused the death of a child. Seismic activity (earthquakes) continued until 8 December, when they stopped abruptly.

On 28 May 2006 a lava fountain was observed in the caldera, which persisted till the 31st. This was accompanied by a rise in seismic activity, and a red cloud seen over the summit, reaching a height of 3 km. Earthquake activity rose sharply again in October, causing local authorities to issue an evacuation warning, but no eruption followed.

On 12-13 January 2007 a series of tremors were felt on the island, and an ash cloud was seen over the summit, again a lava lake was seen to have formed in the caldera.

View of the lava lake in the caldera of Mount Karthala on 31 May 2006, taken during a South African Army fly over of the summit. Juile Morin/Volcan-Actif.

The Comosos Islands are considered to be hotspot volcanoes, located over a magma plume which originated deep in the Earth's mantle which is rising through the overlying African Plate, though they may be connected to the East African Rift Zone, which extends from the Red Sea to the coast of Mozambique, roughly a thousand kilometers southwest of the Comoros.

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