Tuesday, 18 October 2016

When the earth moves under your feet, a blog post by Richard Abbott

In Britain, we're used to history - and historical fiction books - where the terrain is basically the same as today. The human presence on the surface might well change, so that towns and cities grow, old buildings turn to ruins, rough tracks turn into railway lines, and so on. Or we might alter the clothing of vegetation - marshes are drained, forests felled, or fertile land turns to peaty bog. But we generally feel here in England that the bones of the landscape itself remain the same on a human timescale. We expect the land to change form only over geological timescales.

Mt St Helens before and after (USGS images)
Other people though, in other parts of the world, have a different expectation. Earthquakes, volcanoes and tsunamis can not only cause loss of life or damage to property, but can reshape the terrain. Mount St Helens was reckoned to be one of the most attractive of the Pacific Rim volcanic cones until May 18th 1980, when the eruption removed over 1/8 of the volume of the former cone. Iceland gained a new island in November 1963, when Surtsey emerged from the waves as a result of subterranean action.

But often we Brits think of that as something which happens in other lands. But actually there are signs of change in counties like Norfolk and Lincolnshire. Near to Cromer, several villages named in the Domesday Book or other more recent records are now up to half a kilometre out to sea. There is evidence that the Lincolnshire coast was, until the 13th century, protected by a chain of offshore barrier islands. The demise of these in a series of storm surges drastically altered the coastline and its vulnerability to the sea. But despite these signs here in our own land that our not-so-distant ancestors walked across a different landscape, it takes a bit of adjustment.

The geology is quite straightforward. During the last ice age, a little over 10000 years ago, a hugely heavy layer of ice pressed the land downwards, to a greater degree in the colder north than the warmer south. When the ice melted, two things happened. The sea level rose because of extra water. But also the land shifted. The land in places where the ice had been heaviest started to lift up. Outside that, further south, it started to sink down. Try placing a heavy book on a soft cushion and you'll see the effect in action.

Now, 8000 BC is not all that long ago, really - the Neolithic Age, and so the beginnings of recognisably complex society started not all that much later, around 5000 BC. And although the vertical movement of land in any one year is tiny - perhaps a few millimetres - over the course of a century it adds up. Our Neolithic and Bronze Age ancestors in some parts of the country experienced quite different terrain.

Aerial view of the Scilly Isles (Wiki)
In the north, where the land has lifted, we find settlements which used to be on the coast now stranded well above the waterline. Stone circles at the southern end of Coniston Water, in Cumbria, used to be close to an arm of the sea reaching in from Morecambe Bay, but are now over five miles from the coast.

But in the far south, in the Scilly Isles, we see an even more dramatic change as the land sinks down. During the Bronze Age, when many of the prehistoric monuments were being built, there was basically a single large island. Around that, especially to the west, there were a few scattered outposts including what we now call St Agnes, Annet, and the Western Isles. The whole central area, now a submerged area in which quite large vessels can anchor if they find the deep patches, was then a fertile plain supporting crops and animals.

Tidally submerged field wall, Samson, Scilly Isles
All that has gone - perhaps spawning tales of Lyonesse or Atlantis - but its passing has been recorded in history. Even now, low tide allows careful explorers to go well beyond the shoreline, disturbing herons and other wading birds browsing what has been left in the seaweed and rock pools. You pass by the remains of stone walls which presumably served as boundary markers, but are now submerged much of the time. At especially low spring and autumn tides, tall people can still cross between most of the islands without swimming - so long as you know where the sand bars and shallow patches are.

As well as simply projecting backwards the change in sea level, at a rate of 30 centimetres per century, we can look back at history. We know that in 1127, Tresco and Bryher were still a single island, with the two names referring simply to internal parish divisions. By 1600 they were separate, and the Grimsby Sound between them had become a sheltered haven for ships. The transition did not take many generations, and you have to wonder what the occupants made of the stories of their ancestors.The central area between St Mary's and the northern cluster of islands probably flooded around 6-700AD. On the other side of the country, ship burials were happening at Sutton Hoo.

But a change of 30 centimetres per century disguises the more dramatic way in which these events unfolded. This figure comes into perspective when you remember that the tidal range in a big spring tide on Scilly is around six metres. During a winter storm, waves coming across the Atlantic sometimes break over the top of the Bishop Rock lighthouse, some fifty metres high. The changes to separate island from island have not always been the result of a steady trickle of rising water; some will have been dramatic, cataclysmic events.

Samson, Scilly Isles - still one island at present...
This continues to happen today. It used to be reckoned that there were 146 islands in the archipelago, where an island is defined as a body of land separated at high tide and able to support vegetation of some kind. A few winters ago, this became 147, when a severe storm broke through a thin land bridge at Rushy Bay, Bryher, and converted a peninsula into an island. You look at some places as you walk around, and wonder how long they will remain attached.

From a fictional point of view, these kinds of gradual changes to the land itself offer a new storytelling dimension. Authors have explored - and I hope will continue to explore - sudden changes like the eruption of Vesuvius, or various earthquakes. Gradual change has not, I think, been used nearly so often. It could perhaps make for an interesting historical plot based on prehistoric Doggerland, in today's North Sea. Or a speculative fiction story where diminishing land serves as a variation on resource failure. It's worth remembering that the terrain we see today is not eternally fixed - even in this green and pleasant land - and has its own changing history.

About the author:
Richard Abbott is one of the reviewers at The Review, and lives in London, England. He writes science fiction about our solar system in the fairly near future, and also historical fiction set in the ancient Middle East - Egypt, Syria, Canaan and Israel.

When not writing words or computer code, he enjoys spending time with family, walking, and wildlife, ideally combining all three pursuits in the English Lake District. He is the author of In a Milk and Honeyed LandScenes From a LifeThe Flame Before Us - and most recently Far from the Spaceports. and Timing. He can be found at his website or blog, on Google+GoodreadsFacebook and Twitter.

1 comment:

  1. A great post from Richard, our resident geologist! Very insightful, it's quite disconcerting to think that we have lost some of our Domesday villages to the sea!