0:00:29 > 0:00:31I'm on the coast of Eshaness,
0:00:31 > 0:00:33one of the most remote spots in the British Isles.
0:00:33 > 0:00:38One one side, hundreds of acres of bog and moor.
0:00:38 > 0:00:40On the other side, the North Atlantic.
0:00:40 > 0:00:44Between and sea and the land, a narrow coastal battleground.
0:00:44 > 0:00:47On the defence, the ancient rocks of Shetland,
0:00:47 > 0:00:51on the attack, the power of waves.
0:00:55 > 0:00:58This is the Grind o' da Navir.
0:00:58 > 0:01:03The rock was created millennia ago by a volcanic lava flow.
0:01:03 > 0:01:05Now, all that remains of the clifftop
0:01:05 > 0:01:09is a spectacular amphitheatre hewn out of the rock
0:01:09 > 0:01:11by gigantic storm waves.
0:01:13 > 0:01:16I want to know how the titanic battle between sea and rock
0:01:16 > 0:01:18reshapes this coast.
0:01:24 > 0:01:26This coast is strewn with clues,
0:01:26 > 0:01:30clues which reveal the terrifying power of the sea.
0:01:30 > 0:01:32You just have to know where to look.
0:01:36 > 0:01:40'Across the loch from one of the UK's biggest oil terminals,
0:01:40 > 0:01:43'I'm on the hunt for signs of a cataclysmic event
0:01:43 > 0:01:46'which hit these islands thousands of years ago.'
0:01:48 > 0:01:50Thanks, Mick!
0:01:50 > 0:01:54'Apparently, the evidence is hidden in the peat banks of Sullom Voe.'
0:01:54 > 0:01:57- Lovely beach you've brought me to, Adrian.- Oh, yes!
0:01:57 > 0:02:01'Geomorphologist Adrian Hall is going to show me what to look for.'
0:02:03 > 0:02:05- This is peat.- Well, I know that!
0:02:05 > 0:02:09Yes! It's got a wonderful environmental history locked in here.
0:02:09 > 0:02:12- The turf up here with the modern vegetation...- Where we are today.
0:02:12 > 0:02:15And here we've got the dried-out peat.
0:02:15 > 0:02:17And then we've got some very clear layers in the peat,
0:02:17 > 0:02:19and then when we get down to about here,
0:02:19 > 0:02:23we've got a very, very clear change. It's mainly sand,
0:02:23 > 0:02:26- but as you can see, there are lumps of gravel.- Yeah. Sudden change
0:02:26 > 0:02:28of colour, isn't there? And texture.
0:02:28 > 0:02:31But even more striking are these lumps of peat
0:02:31 > 0:02:33which clearly have been torn up
0:02:33 > 0:02:35from some pre-existing peat bank.
0:02:36 > 0:02:38Let's just have a look at that.
0:02:38 > 0:02:41See, the sand layer is really quite thick.
0:02:41 > 0:02:44It's got tiny marine organisms in it,
0:02:44 > 0:02:47so we've got to have a process that brings this material from the seabed
0:02:47 > 0:02:50- and up onto the land.- So what is it? - There's only one thing
0:02:50 > 0:02:54that can produce deposits of sand 20 metres above sea level
0:02:54 > 0:02:57- and that's a tsunami.- A tidal wave? - A tidal wave.
0:02:57 > 0:03:00The sand layer buried in this peat
0:03:00 > 0:03:05is evidence of a tsunami that hit this coastline 7,000 years ago.
0:03:05 > 0:03:06It was caused
0:03:06 > 0:03:09by a gigantic underwater avalanche
0:03:09 > 0:03:11on the continental slope off Norway.
0:03:11 > 0:03:14When a mass of sediment collapsed onto the seabed,
0:03:14 > 0:03:20it generated killer waves destined for Shetland 250 miles away.
0:03:21 > 0:03:23The first hunter-gatherers
0:03:23 > 0:03:26were already on Shetland 7,500 years ago,
0:03:26 > 0:03:29so we've got to imagine this as a broad open valley,
0:03:29 > 0:03:31the sea far, far out there.
0:03:31 > 0:03:35And then suddenly, on the horizon, there would be a wall of water,
0:03:35 > 0:03:37and it would be moving very rapidly.
0:03:37 > 0:03:42- So it funnelled down Sullom Voe, got constrained between the two shores. - It would build
0:03:42 > 0:03:46and grow until, eventually, you were looking at a wall of water
0:03:46 > 0:03:4720 metres high.
0:03:50 > 0:03:54And then it would break and surge forward into this area,
0:03:54 > 0:03:58carrying the debris and hurling it against the land.
0:03:58 > 0:04:04The low-lying parts of Shetland would have been completely overwhelmed.
0:04:04 > 0:04:09This ancient tsunami reached as far south as the English border.
0:04:11 > 0:04:14The tsunami which struck these islands was a freak event,
0:04:14 > 0:04:18but the waves being generated by North Atlantic weather patterns are not,
0:04:18 > 0:04:20and they can be just as ferocious.
0:04:20 > 0:04:23Big waves are going to reach further inland.
0:04:23 > 0:04:27Life on the edge could get a lot more precarious.