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The IODP drill ship JOIDES on a calm night northeast of New Zealand. (Photo: David Buchs)

Volcano voyage seeks truth about hotspots

  • BY Marina Kamenev |
  • February 21, 2011

Deep-sea volcanoes created by hotspots are helping scientists understand the movement of Earth's continents through history.

A RECENT EXPEDITION TO a great chain of underwater volcanoes 1500 km north-east of New Zealand may provide new insight into the geography of the Earth millions of years ago.

Scientists sailed to the Pacific to find out whether or not hotspots – plumes of superheated molten rock – in the Earth's mantle are in fact stationary, as current theory suggests. These hotspots create chains of volcanoes as tectonic plates move over the top of them.

"The research will shed light on the dynamic processes of the Earth's mantle," says Dr David Buchs, a geologist at the Australian National University, in Canberra. David was a member of the international expedition which spent two months on the Pacific Ocean from 17 December, 2010 to 11 February, 2011.

Drilling into Louisville Seamount Trail

The target of the expedition was the 4,300 km-long Louisville Seamount Trail of underwater volcanoes, which are all between 1200 m and 2000 m below the surface. The Louisville volcanoes were formed between 80 and one million years ago when the Pacific oceanic plate passed over a hotspot in the Earth's mantle.

Little is known about the hotspot itself, and the expedition – part of the The Integrated Ocean Drilling Program (IODP), a massive global research effort involving hundreds of academics in 20 countries – drilled into five of the Louisville volcanoes in an attempt to learn more about the forces that created them.
 
Using equipment lowered from the IODP flagship research vessel, the JOIDES Resolution, the researchers drilled 500 m down, extracting large amount of volcanic rock and fossils for analysis.

Until recently, experts thought that volcanic hotspots stayed in the same place in the Earth's mantle and that chains of volcanoes only formed when the Earth's tectonic plates moved across them. This process is credited with forming a chain of now-extinct volcanoes down the east coast of Australia (which includes the Glass House mountains and the Warrambungles) and also the Hawaiian islands.

Volcanic hotspots on the move

Whether or not hotspots move is an important distinction, because they are used as markers to map the movement of Earth's continents through geological history. However, recent research suggests that the hotspot which created the Hawaiian islands may have moved.

"The hotspot that created the Hawaiian-Emperor chain of volcanoes to the north of the Louisville Seamount Trail might not have been stationary, but moved about 15 degrees southward between 80 million and 50 million years ago," says geologist and expedition member Dr Benjamin Cohen, at the University of Queensland in Brisbane.

The researchers hope to use the samples collected, over the next six months, to test whether or not the hotspot under the Louisville Seamount Trail has also moved. This will help to confirm if the movement of the Hawaiian hotspot represents a wider trend.

Clues to past climate in volcanic rock

"This study is critical to understanding the Earth's movements over time," comments Dr Mark Tingay a geologist at the University of Adelaide who was not involved in the expedition. "We have used hotspots as a reference frame, with the assumption that they are fixed in place and stationary. If they have moved then it's very valuable to know how, in terms of geographically [mapping] the Earth to what it was millions of years ago."

These rock samples will not only be used to analyse the way the Earth was shaped, but will also reveal key information about past climate. "The fossils will help us to understand oceanographic conditions ... [and] the climate in the past," says David. "This information could be valuable for looking at the way the climate is changing now."

The nine-nation expedition was led by scientists from Oregon State University in the US, and both the National Institute of Advanced Industrial Science and Technology and the Geological Survey in Japan.

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