Nicholas Crane discovers evidence of a giant tsunami, a tidal wave which devastated Britain and reshaped the Shetland coast about seven thousand years ago.
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I'm on the coast of Eshaness,
one of the most remote spots in the British Isles.
One one side, hundreds of acres of bog and moor.
On the other side, the North Atlantic.
Between and sea and the land, a narrow coastal battleground.
On the defence, the ancient rocks of Shetland,
on the attack, the power of waves.
This is the Grind o' da Navir.
The rock was created millennia ago by a volcanic lava flow.
Now, all that remains of the clifftop
is a spectacular amphitheatre hewn out of the rock
by gigantic storm waves.
I want to know how the titanic battle between sea and rock
reshapes this coast.
This coast is strewn with clues,
clues which reveal the terrifying power of the sea.
You just have to know where to look.
'Across the loch from one of the UK's biggest oil terminals,
'I'm on the hunt for signs of a cataclysmic event
'which hit these islands thousands of years ago.'
'Apparently, the evidence is hidden in the peat banks of Sullom Voe.'
-Lovely beach you've brought me to, Adrian.
'Geomorphologist Adrian Hall is going to show me what to look for.'
-This is peat.
-Well, I know that!
Yes! It's got a wonderful environmental history locked in here.
-The turf up here with the modern vegetation...
-Where we are today.
And here we've got the dried-out peat.
And then we've got some very clear layers in the peat,
and then when we get down to about here,
we've got a very, very clear change. It's mainly sand,
-but as you can see, there are lumps of gravel.
-Yeah. Sudden change
of colour, isn't there? And texture.
But even more striking are these lumps of peat
which clearly have been torn up
from some pre-existing peat bank.
Let's just have a look at that.
See, the sand layer is really quite thick.
It's got tiny marine organisms in it,
so we've got to have a process that brings this material from the seabed
-and up onto the land.
-So what is it?
-There's only one thing
that can produce deposits of sand 20 metres above sea level
-and that's a tsunami.
-A tidal wave?
-A tidal wave.
The sand layer buried in this peat
is evidence of a tsunami that hit this coastline 7,000 years ago.
It was caused
by a gigantic underwater avalanche
on the continental slope off Norway.
When a mass of sediment collapsed onto the seabed,
it generated killer waves destined for Shetland 250 miles away.
The first hunter-gatherers
were already on Shetland 7,500 years ago,
so we've got to imagine this as a broad open valley,
the sea far, far out there.
And then suddenly, on the horizon, there would be a wall of water,
and it would be moving very rapidly.
-So it funnelled down Sullom Voe, got constrained between the two shores.
-It would build
and grow until, eventually, you were looking at a wall of water
20 metres high.
And then it would break and surge forward into this area,
carrying the debris and hurling it against the land.
The low-lying parts of Shetland would have been completely overwhelmed.
This ancient tsunami reached as far south as the English border.
The tsunami which struck these islands was a freak event,
but the waves being generated by North Atlantic weather patterns are not,
and they can be just as ferocious.
Big waves are going to reach further inland.
Life on the edge could get a lot more precarious.