Thursday 1 November 2012

Volcanic activity on Heard Island.

Heard Island is a remote volcanic island on the Kerguelen Plateau in the southern Indian Ocean. It is made up of two volcanoes, the larger Big Ben to the southeast and the smaller Mount Dixon to the northeast. The crater of Big Ben forms a 5-6 km wide caldera, breached to the southwest, with a second smaller volcano, Mawson Peak, within. The summit of Mawson Peak forms the highest point on the island, at 2475 m above sea-level (it is also technically Australia's highest mountain). This is considered to be an active volcano, though little is known about its activity due to its remote location and covering of glaciers.

Composite Satellite image showing the position of Heard Island and the Kerguelen Plateau. Google Maps.

Heard Island seen from the sea. Heard Island Solo.

On 21 and 24 September and 10 and 19 October satellites passing over Heard Island detected thermal anomalies, suggesting that a an eruption could be occurring on the island. A visual image captured by NASA's Earth Observing-1 satellite on 13 October 2012 may support this, though it is not completely clear. The summit appears to show reduced snow cover and there is a dark area within the crater which may indicate fresh lava. The island is covered by cloud for much of the time, making these observations rare.

(Top) Earth Observing-1's 13 October image of Heard Island. (Bottom) An image taken in February 2009 from the International Space Station for comparison. Not the more defined shape of Mawson's Peak in the upper image, implying melting of snow cover. NASA/Earth Observatory.

The Kerguelen Plateau is an underwater volcanic large igneous province formed by volcanic activity starting about 110 million years ago. It has sedimentary rocks which suggest the bulk of the plateau may have been above the sea for much of this time, sinking about 20 million years ago, causing some to consider it a submerged continent. The volcanic activity is thought to come from a hotspot created during the breakup of the Gondwanan continent in the mid-Cretaceous. The landmass may once have been continuous with Australia and India; it is thought that in the Cretaceous it would have formed a microcontinent largely covered by vast coniferous woodlands. Most of the plateau is now about 600 m below sea-level.

Map showing the positions of the parts of the former Gondwanan continent in the Late Cretaceous, 85 million years ago. Kerguelen is highlighted in orange. Ali & Aitchison (2009).

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