Researchers use new method to date lava flows
To better understand the formation of the Earth's crust, scientists at the GEOMAR Helmholtz Centre for Ocean Research Kiel have used new technology to date the lava flows at the Northern Kolbeinsey Ridge, about 500 kilometres from Iceland. In doing so, they found evidence of large deepsea volcanic eruptions, which were likely to have been responsible for almost half of the Earth's crust.
Situated at the Mid-Atlantic Ridge, the eruptions of the Icelandic volcanoes Eyjafjallajökull and Bárðarbunga have left us with breath-taking images, while giving rise to the creation of new material for the Earth's crust at the mid-ocean ridges. This study contains new evidence showing that eruptions in the vicinity, many times larger than those recently observed on Iceland, are likely to be responsible for almost half of the Earth's surface.
"About 70 percent of the surface of the Earth was formed by volcanic eruptions at mid-ocean ridges, where depressurisation in the mantle underneath the ridge allows melts to form and travel up to the seafloor where they erupt, so what we're doing here is trying to understand the fundamental processes that created our planet,“ said Dr Isobel Yeo, lead author of the study.
Details of the team's discovery would be published in an upcoming issue of the international journal Earth and Planetary Science Letters.
"The tectonic plates move at different speeds, but most of the time they are moving slowly apart and where this happens lava can't easily reach the seafloor. While we have some good estimates and hypotheses, the frequency and size of these eruptions, which are occurring under the oceans globally, is basically unproven, “ said Dr Yeo.
Now, by using a new method, the researchers are able to survey and date the young lava flows on a portion of the Mid-Atlantic Ridge, and found out episodic eruptions had taken place.
The new method, used for the first time on an expedition aboard the German research vessel POSEIDON, utilises acoustic data of the seafloor obtained by the autonomous underwater vehicle (AUV) ABYSS and the records from sediment cores collected in the area. This allows the seafloor to be surveyed without damaging the terrain.
"In the past, we have used the AUV predominantly for mapping the seabed, but now we can also use it to determine the age of young lava fields," said Dr Yeo.
The researchers could determine the exact position of the mid-ocean ridges in the region using the new data.
Dr Yeo also asserted that the amount of lava found over the years (which generated 18 lava flows) would not have been sufficient to maintain the normal crustal thickness of seven to ten kilometres in the region: "Over the last 8,000 years, we see at least 5,000 years with no volcanic eruptions whatsoever and what we do see the rest of the time isn't nearly enough. This means there must be periods of much higher volcanic activity, probably with volumes tens of times as large as those observed during recent Icelandic eruptions."
Much of the global mid-ocean ridge system has not been mapped, with very few detailed studies been done to date. Thus, this new research method has important implications and opens up new possibilities for future research.
Link to study: www.sciencedirect.com/.../S0012821X16000510