Remnants discovery sheds light on landslide activity
Scientists in Denmark and the United Kingdom have unearthed the remnants of the world's best preserved examples of a massive ancient landslide in Spain. Their finding, presented in the journal Geology, gives volcanologists the information they need to determine when the landslide occurred following a large volcanic eruption on the Canarian island of Tenerife. Scientists welcome the news because little information is known about why such landslides occur.
The sea engulfed the southeast slopes of Tenerife 733 000 years ago after they collapsed during a volcanic eruption. But not all was lost. Volcanologists at the University of Leicester in the United Kingdom and Roskilde University in Denmark have found the onshore remains of this landslide amid canyons and ravines of Tenerife's desert landscape. This landslide deposit is up to 50 metres thick. But the researchers suggest it may extend another 50 kilometres offshore.
'It is one of the world's best-preserved accessible examples of such an awesome phenomenon,' says Dr Mike Branney from the Department of Geology at the University of Leicester, one of the authors of the study, 'because the debris from such landslides mostly spreads far across the deep ocean floor, inaccessible for close study.'
Dr Branney notes how the Tenerife rubble is comprised of blocks of lava that chilled quickly as the volcano erupted. Thanks to the radioactive materials found within them, Michael Storey at Roskilde was able to pinpoint the date for this natural catastrophe.
'Climate change is often invoked as a trigger by pushing the side of the volcano outwards,' explains co-author Dr Storey, head of the Quaternary Dating Laboratory, Department of Environmental, Social and Spatial Change at Roskilde University. 'In the shattered landscape that remained, lakes formed as rivers were dammed by debris, and the change to the shape of the island altered the course of explosive volcanic eruptions for hundreds of thousands of years afterwards.'
While such phenomena are not frequent they are common, according to the scientists. It is important to understand such phenomena because their effects influence areas beyond this Canarian island. The researchers note how tsunamis generated from such events may travel to devastate coastlines thousands of miles away.
'Understanding the Earth's more violent events will help us be prepared, should repeat performances threaten,' the researchers say.
Dave Petley, who writes the 'Landslide Blog' of the American Geophysical Union, says such landslides occur around four times every century. The remains are spread out over the ocean floor. Concerning the deposit, it contains classic debris avalanche material and shattered blocks in a highly disrupted, unsorted matrix.
Dr Petley, who is a professor at the Department of Geography at Durham University in the United Kingdom, says this is typical of a highly energetic, major collapse event.
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