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29 Aug 2007

The Rise and Fall of Sea Levels and Civilisations.

sc1Just back from a few glorious days on the Scilly Isles, somewhere I have never been before, but will certainly go back to. What a beautiful place. For those who don’t know, they are a small collection of islands off the south west coast of Cornwall, about 45km west of Land’s End. They were formed as part of a collision between continental plates 200 to 300 million years ago, which forced up granite intrusions, which over time have eroded, leaving the landscapes which run from Dartmoor, down through Cornwall and then out under the sea, rising to put in a last appearance at the Scillies. As well as being a stunningly clean and beautiful place, being there also focused my mind on sea level rise, as the rising and falling of the sea has been central to the evolution of culture and ecology there over time.

scDuring the most recent Ice Age, (about 18,000 years ago) the sea level around the Scillies was as much as 75 metres lower than it is now. What we see now as individual islands were, as recently as 3,000 years ago, one single island. In one shop I saw this beautiful poster (I didn’t see it anywhere else as postcards, hence my not that good photo of it, right) which, through the clear blue (but unfortunately freezing) waters surrounding the island allow one to see the underwater landscape around the islands.

Indeed, there are legends in both Scilly and Cornwall of a lost land between the two, called Lyonnesse. Legend tells of a land of rich pastures, abundant orchards, beautiful people and a city called Lions. It was said that from its highest point you could count the steeples of 140 churches. Legends persist of sailors being able to still occasionally hear the bells tolling beneath the waves, and there is apparently a family in Cornwall, called Trevelyan, who claim to be related to the only man who escaped the inundation, he scrambled out on his horse, which lost a shoe in the flight; their family crest featuring 3 horseshoes.

It is thought that much of this legend is to do with the Bronze Age inhabitants of the islands who first arrived there 4,000 years ago when they were all connected. Their submerged field walls and round houses, some of which can still be seen at low tide, may well have been what inspired the storytellers to begin to weave the legends of Lyonnesse.

sc2When you walk around the Scillies now, one is struck that what appear to be islands, are in fact the tops of mountains, and that the direction of history and climate means that they will, in time, go the way of the homes of their Bronze Age ancestors. Hugh Town, the main settlement on the main island, St. Mary’s, is perilously close to sea level, being just a few feet above the sea.

One night in the hotel we stayed in, we watched a fascinating programme about India and its pre-Raj history. It built up, through DNA analysis, archaeology and climatic reconstruction, a compelling case that present day India came from a civilization in the Indus valley, now long gone, which was forced to migrate east when the rivers on which they depended dried up. Their argument that climate is one of the principle drivers behind settlement resonated as we sat there on the Scillies.

If we fail to prevent runaway climate change, what tales will be told of our civilizations the lie beneath the waves? Will we be talked about by future inhabitants of this earth as having been strong and beautiful with rich pastures and abundant orchards, or as a society whose greed and inactivity brought about its own demise? What legends might those on the high ground of the Peak District tell of the now-flooded lowlands of East Anglia? Sitting on the beach in Scilly, looking out across the islands, looking down into the waters, sea level rise felt very present and an integral part of our genetic memories.

By the way, if you’re thinking “miserable git… goes to the Scilly Isles and spends the whole time fretting about sea level rise”, it was an occasional muse… I also spent a lot of time doing other things! I blame the trip over to the Scilly Isles on the boat, which for the nervous sea traveller does begin to get one thinking apocalyptic thoughts… while walking around the boat, feeling seasick and altogether queasy, I came across, in the lounge, a poster called “Shipwrecks of Scilly”, a map of all the shipwrecks on the rocks around the islands (there have been many). Luckily the crossing was relatively smooth.

Categories: Climate Change

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29 Aug 10:07am

I also watched that show on India, really interesting. I was wondering if the fall of the Sumerian Empire and their potential migration fallout may also have had an influence on the subsequent collapse of the Indus Valley Civilization and their migration. The two events appears to be in a similar 300 odd year period. There was also a fascinating show on finding a lost city of Egypt a while back. They found it by looking at where the delta rivers were located in the past and summised that that particular Egyptian dynasty collapsed because they invested so much into trying to preserve their capital city against the shifting river. This obviously points to the need to view climate and ecology as the fundamental dictators on civilization and that adaptation through a balance of decentralised power and freemdom for self-organisation are key. Now there is talk of building another Thames barrier and i wonder if these lessons will ever be learnt when each generation fights to maintain view of a static world.

29 Aug 1:39pm

Nice piece, Rob.

Sudden sea level rise is one of my obsessions these days, too.

I often see the increasingly unstable Greenland ice cap as a Damocles’ sword – ready to deliver a sudden (in geological terms) – and from a Gaian viewpoint, not unwelcome – coup-de-grace to our civilization should we fail to make radical changes to halt climate change.

I live at sea level (in a 3rd floor flat) and I have thought of painting a blue line on the housefront 7m above sea level to draw attention to the fact.

29 Aug 8:51pm

I stumbled on a book linked to this,

My Dad is an amateur inter tidal archaeologist with a bit of a thing about sea levels.

On his bookshelf was a book called “Floods, Famines and Emperors, El Nino and the fate of Civilisations” by Brian Fagan.
I ‘borrowed’ it.
I cannot fully comment on it as I haven’t finished reading it yet.

The general gist is a link between global weather patterns and the coming and going of civilisations and or historic events.

So far not a bad read.

If Robert needs a hand marking his blue line let me know, we have the technology

31 Aug 2:59pm

The question I have is this: “What would the political and social environment be like if the sea was rising every year without knowing why or how?” We see that many ancient civilizations ended up living in hostile high altitude areas and we have wondered why they would do so, with perfectly good fertile land surrounding them below. Perhaps it was because they thought the sea was going to continue rising, and they wanted to get as far from it as they could.

6 Sep 10:24am

An interesting piece, stories of lost cities and lands taken by the sea such as Lyonnesse, Cantref Gwaelod and Atlantis never fail to excite the imagination.

The only problem the article has is that it fails to distinguish between eustatic and relative sea level changes that would have both influenced the landscape of the Scilly Isles at the end of the end of the Late Devensian.

Let me explain:

Eustatic sea level change is sea level change that effects the entire world i.e. under stadial conditions more water is held in ice sheets, glaciers and permafrost so the sea level is low; and during interstadials less water is held in ice sheets, glaciers and permafrost so the sea level is higher, simple.

Relative sea level change is caused by local forces and only affects a limited area. In the case of the Scilly Isles at the end of the last ice age the major influence on sea level in the area was the weight of the British Ice sheet on the earths crust. Ice sheets are heavy, and when this weight is loaded onto an area of crust it deforms it forming a depression under and close to the margins of the ice sheet. Around the margins of the depression the crust is displaced upwards, raising it above its previous level. This is the forebulge effect and it can extend several hundred miles from the depression (the extent is determined by how large the depression is i.e. the greater the depression the greater the displacement). When the ice sheet melts, the weight of the ice is removed from the crust and so the crust will slowly make its way back to the state of equilibrium that it was at before it was loaded with ice (generally speaking this state of equilibrium is never reached as usually another ice age will occur before it can do so). This process is known as glacio-isostacy.

The Scilly Isles sit on the forbulge created by the Late Devnsion Ice sheet which is still in the process of correcting itself i.e. it is in effect sinking, causing a relative rise in sea level around the islands. It would have been this process combined with eustatic changes caused by the melting of the ice sheets, that would have been the cause of the inundation the lands inhabited by people during the Bronze Age. It is therefore inappropriate to consider sea level change around the Scilly Isles in the general terms used here as relative sea level change effects different parts of Britain in different ways, in some areas sea level is lowering (this is particularly obvious in Scotland), while in others it is rising (the south).

This doesn’t help the Scilly Isles though, they are potentially extremely vulnerable.

24 Sep 9:20am

Very entertaining story and ensuing discussion.

I live on the Queen Charlotte Islands in BC, Canada, an area which has also experienced the effects of glacial depression and rebound. And as the Pacific Plate slides alongside us, we are slowly dragged about two inches a year towards Alaska !

Nadia Hillman
27 Sep 10:15pm

Is Totnes not destined to slide into the sea anytime soon? Only I think I might like to retire there you see!