Thursday, 5 November 2015

Eruption on Heard Island.

A United States Air Force satellite detected an ash plume above Heard Island, an uninhabited volcanic island roughly in the Southern Ocean, midway between Madagascar, Antarctica and Australia on Friday 30 October 2015. This is the first activity detected on the island since 2013, though the island is so remote that activity in the intervening time cannot be ruled out.

The approximate location of Heard Island. Google Maps.

Heard Island is part of the Kerguelen Plateau, a sunken microcontinent roughly 3000 km to the southwest of Australia, which is believed to have been part of the ancient supercontinent of Gondwana prior to its breakup. Most of the microcontinent is now an average of 600 m below the sea surface but the volcanic Kerguelen Islands plus the Heard and MacDonald Islands still rise above sealevel. Volcanism on the plateau began during the breakup of Gondwana, with the formation of the Kerguelen Hotspot between the landmasses that went on to become India and Antarctica, and is still going on to a minor extent on Heard and MacDonald Islands. The area is thought to have been covered with Conifer forests during the Cretaceous, and the islands still host unique floral communities.

Plate reconstructions of the southern Indian Ocean region. Red stars = possible reconstructed positions of the Kerguelen Hotspot; those labeled “K” assume that the Kerguelen archipelago is the current location of the Kerguelen hotspot, and those labeled “H” assume that Heard Island is the hotspot’s current location. Black shading = magmatism associated with the Kerguelen Hotspot, diamonds = lamprophyres (labeled with “L” in 110 Ma panel) as they have appeared through geologic time. Dashed line = a possible northern boundary for Greater India. IND = India, ANT = Antarctica, AUS = Australia. (A), (B) Seafloor spreading initiated at ~133 Ma between Western Australia and Greater India and at ~125 Ma between Australia and Antarctica. This model assumes breakup between India and Antarctica at ~133 Ma, although the timing of this event is not well known. The Bunbury Basalt (BB) of Southwest Australia erupted close to these breakup events in both time and space. Continental portions of Elan Bank (EB) and the Southern Kerguelen Plateau (unknown dimensions) remained attached to Greater India at these times. The Naturaliste Plateau (NP) also contains continental crust. (C), (D) Seafloor spreading continued between India, Antarctica, and Australia. The initial massive pulse of Kerguelen magmatism created the Southern Kerguelen Plateau (SKP), the Rajmahal Traps (RAJ), and Indian/Antarctic lamprophyres (L) from ~120 to ~110 Ma (Fig. F3, p. 38) and may be linked to breakup and separation between Elan Bank and Greater India. The Central Kerguelen Plateau (CKP) formed between ~105 and ~100 Ma and Broken Ridge (BR) between ~100 and ~95 Ma (Fig. F3, p. 38). Igneous basement of the Wallaby Plateau (WP) is not well characterized geochemically and has not been dated, but its age is inferred to lie between ~120 and ~100 Ma. (E), (F) The hotspot generated the Ninetyeast Ridge (NER) and Skiff Bank (SB) as India continued its northward drift relative to Antarctica. (G), (H) At ~40 Ma, seafloor spreading commenced between the Central Kerguelen Plateau and Broken Ridge. The hotspot generated the Northern Kerguelen Plateau (NKP), and, since 40 Ma, as Broken Ridge and the Kerguelen Plateau have continued to separate, has produced the Kerguelen Archipelago, Heard and McDonald Islands, and the chain of volcanoes between Kerguelen and Heard. Frey et al. (2003).


See also...

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