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Earth of fire

Actualité volcanique, Articles de fond sur étude de volcan, tectonique, récits et photos de voyage

Publié le par Bernard Duyck
Publié dans : #volcanic activity

A study published this month in Geological Magazine traces the volcanic ascendancy of Lord Howe Island, 600 km offshore of New Wales (east of Sydney).

The geology of Lord Howe has been known for a long time: the island forms a crescent about ten kilometers long and two wide, resulting from the erosion of a shield volcano dated 7 million years ago.

Mount Lidgbird and Mount Gower, respectively 777 and 875 meters high in the south of the island, consist of basalt, the remains of lava flows that once filled an important caldera. The end of volcanic activity dates back to 6.4 million years ago.

Located at 31 ° S South, the coral reef is the southernmost in the world.

Lord Howe island and its lagoon and coral reef - photo Australia a la carte - one click to enlarge

Lord Howe island and its lagoon and coral reef - photo Australia a la carte - one click to enlarge

Lord Howe seen from space station - photo ISS006-E-5731 / NASA Johnson Space Center.

Lord Howe seen from space station - photo ISS006-E-5731 / NASA Johnson Space Center.

The Lord Howe Group of Islands includes 28 islands, islets and rocks. Among these, Balls Pyramid, a rocky island 551 m high. colonized by birds.

To the north, the Admiralty group consists of seven small uninhabited islands; to the east, Mutton bird island and Blackburn (or Rabbit) island in the lagoon.

Pyramid Balls is a 552 m high volcanic pinnacle located 24 km south of Lord Howe Island - Gosford sailing club photo

Pyramid Balls is a 552 m high volcanic pinnacle located 24 km south of Lord Howe Island - Gosford sailing club photo

The sub-tropical humid climate is marked by a rainfall rate of 1717 mm. per year, which has allowed the establishment of forests with affinities with Australian, New Caledonian, and even New Zealand flora.

Its isolation is responsible for a strong endemism marking the flora and fauna; 105 plant species out of the 241 native species are endemic. Among the avifauna, seven endemic species have become extinct; four endemics remain: Lord Howe's Zostererops (Zosterops tephropleurus), Woodhen (Gallirallus sylvestris), Golden Whistler (Pachycephala pectoraliscontempta) and a Sparrow, Lord Howe Currawong (Strepera graculina crissalis).

Seabirds massively use these islands as a nesting site, as on Balls pyramid.

 The Woodhen (Gallirallus sylvestris) - endemic to Lord Howe - photo Granitethighs

 The Woodhen (Gallirallus sylvestris) - endemic to Lord Howe - photo Granitethighs

Lord Howe is part of the chain of submarine volcanoes, distant from each other and of different ages, stretching more than 1,500 kilometers to the north, to Mount Horsehead, formed 28 Ma ago.

These volcanoes originated from the displacement of the Australian plate over a stationary hotspot, and the seamounts are the marks of the activity of this hot spot on the tectonic plate.

The volcano chain is part of the Lord Howe Plateau, itself part of the underwater continent named Zealandia.

The total volume of lava erected along the Lord Howe range is 320,000 km³; the distinct chemical signature of the analyzed lavas allowed the dating of the aligned volcanoes that form this largely immersed volcanic chain.
 

Location of two chains of submarine and emerged volcanoes off the east coast of Australia, signature of two different hot spots - Doc. Maria Seton / Geophysical and geological characterization of dredge rents from Southern RV Surveyor ss2012_v06 (ECOSATI): hotspot activity in northern Zealandia

Location of two chains of submarine and emerged volcanoes off the east coast of Australia, signature of two different hot spots - Doc. Maria Seton / Geophysical and geological characterization of dredge rents from Southern RV Surveyor ss2012_v06 (ECOSATI): hotspot activity in northern Zealandia

The various volcanoes of the Lord Howe range, and their dating, on the trace of the hot spot (white dotted line) within the boundaries of the Zealandia continent (red dotted line) - from Mortimer et al. (2017b) - Doc. Geophysical and geological characterization of dredgerings RV Southern Surveyor ss2012_v06 (ECOSATI): hotspot activity in northern Zealandia

The various volcanoes of the Lord Howe range, and their dating, on the trace of the hot spot (white dotted line) within the boundaries of the Zealandia continent (red dotted line) - from Mortimer et al. (2017b) - Doc. Geophysical and geological characterization of dredgerings RV Southern Surveyor ss2012_v06 (ECOSATI): hotspot activity in northern Zealandia

"Tracing the ancestors of Lord Howe island" - EarthByte / You Tube video - in The Conversation

Sources:
- The Conversation - How we traced the volcanic underwater ancestry of Lord Howe Island. - link
- Geophysical and geological characterization of dredgerings from Southern RV Surveyor ss2012_v06 (ECOSATI): hotspot activity in northern Zealandia - by Maria Seton & al.
- Linklater, Michelle. (2016). Pastoral and pastoral development at the latitudinal limit of reef development, southwest Pacific Ocean.

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