Ancient tsunami could have struck Falkland Islands

Ancient tsunami may have struck Falkland Islands


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NASA

The Falkland Islands could sooner or later sooner or later face a significant tsunami.

Scientists have discovered evidence of ancient slope failures on the seafloor to the south of the British Overseas Territory.

Computer fashions recommend these underwater landslides would have been able to sending waves crashing on to the Falklands’ shoreline that had been tens of metres excessive.

Fortunately, such occasions solely seem to occur as soon as each million years or so.

That means islanders should not keep awake at evening worrying about them, says Dr Uisdean Nicholson who’s been investigating the problem.

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Media captionUisdean Nicholson: “The tsunami would take about an hour to reach the Falklands”

“But you do want to capture risks at a range of different timescales. So I definitely think we should do more research to understand the different ways these events might be triggered,” the Heriot-Watt University geologist informed BBC News.

‘Landslide manufacturing facility’ on the Atlantic seafloor

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SOURCE: Nicholson et al

  1. Sub-Antarctic Front (SAF) passes via a slim channel on the seafloor referred to as the 54-54 Passage and accelerates to the northwest
  2. The fast-moving jet of water erodes the sting of Burdwood Bank, choosing up silt and sand which it carries westwards
  3. The SAF encounters an offshoot jet generally known as the Sub-Antarctic Mode Water (SAMW) and slows down, dumping its sediment load
  4. Sediment builds on a steep slope on the northern fringe of Burdwood Bank. Eventually, it collapses, maybe shaken by a quake
  5. The underwater landslides generate tsunami that head in direction of the Falkland Islands. Southern shores might witness 40m-high waves

The submarine landslides all occurred in the identical location – on steeply inclined terrain on the sting of a raised area of the seafloor generally known as Burdwood Bank.

Seismic knowledge reveals examples of repeat sediment failure the place mud, sand and silt has tumbled down-slope into deeper waters.

The quantity of fabric concerned for the bigger occasions seems to be round 100 cubic km.

“That’s approximately the same as if you were to cover the whole area of Edinburgh, right out to the bypass, with 400m of sediment. You would cover Arthur’s Seat,” the Scottish scientist defined.

Nearby exploratory drilling by oil firms and scientific expeditions has allowed the workforce, which incorporates the British Geological Survey (BGS) and University College London, to roughly date the sediments and constrain the frequency of the slope failures.

Three or 4 of the “Edinburgh-sized” slides have occurred within the final three million years.

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Getty Images

Image caption

Sense of scale: Arthur’s Seat, the extinct volcano in Edinburgh, is 250m excessive

Everyone is aware of now that sure forms of big earthquake will set off ocean tsunami by pushing up or miserable the column of water immediately above a rupture within the seafloor.

Less effectively recognised is that sudden slumping of sediment in underwater landslides will obtain the identical impact.

A latest instance contains the September 2018 occasion on the Indonesian island of Sulawesi the place a quake set off a variety of submarine slope failures that then directed two-metre excessive waves on the metropolis of Palu.

And in 1998, a submarine landslide despatched 15m-high waves on to Papua New Guinea that killed 2,200 individuals.

Landslide-induced waves will be very massive certainly, particularly near the supply – though their vitality tends to fall off shortly with distance.

The Falklands are about 150km from Burdwood Bank. Even so, the modelling suggests the bigger slope failures might produce waves as excessive as 40m on the territory’s southern shoreline, and maybe as tall as 10m on the capital, Port Stanley.

“We must stress these are old events that we’ve looked at; we don’t want to put the fear of God into people,” stated BGS Prof Dave Tappin. “But the more events and case histories we study – even if they are millions of years old or a hundred thousand years old – the better we can understand not only how such tsunami are generated but also their likely future hazard.”

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Media captionScientists have modelled how submarine landslides might produce a tsunami

One puzzle for the workforce has been to clarify how a specific location on Burdwood Bank was such a prolific “landslide factory”, and the scientists suppose they do now have a persuasive narrative.

It entails the Sub-Antarctic Front (SAF), the northern-most department, or jet, of the Antarctic Circumpolar Current (ACC).

The ACC is essentially the most highly effective motion of water on Earth and the place the SAF skirts the financial institution it may be accelerated in locations in order that it turns into a extremely erosive power.

The entrance might be choosing up sediment at one location after which dumping it at one other.

This accumulation web site, dubbed Burdwood Drift, is the excessive, steep slope evident within the seismic knowledge.

The emplaced silt and sand is clearly rising once more however it’s inconceivable proper now for anybody to say if or when one other slide would possibly happen.

Internal instabilities might ultimately activate the slope, however a extra seeming state of affairs is that shaking from a neighborhood quake provokes a collapse of the sediment. After all, the financial institution is comparatively near tectonic plate boundaries.

Future analysis would contain digging on the Falklands to attempt to discover deposits from historic tsunami.

“You maybe even want to sample the drift to see what it consists of, what the shear strength of the material is; and then you can put all this information into your models to refine them,” stated Dr Nicholson.

The current study is reported in the journal Marine Geology.

Jonathan.Amos-INTERNET@bbc.co.uk and observe me on Twitter: @BBCAmos



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