2012-03-19 03:48:28Sea-level rise 8500 BP to now: a stark example from the coast of Wales
John Mason


Folks, the text below is what I've fired off to The Guardian hoping to get another bit published and a few quid in the bank-account! Would it be adaptable as a SkS post and if so what additional detail would people like to see? I have stacks of data and some neat images. I'll come up with a snappier title if people like the text!

Cheers - John


Borth beach, on the Mid-Wales coast in North Ceredigion, has a well-hidden secret. Every winter, after storms have scoured away parts of its extensive sands, areas of peat appear, littered with fallen tree-trunks and with stumps in growth position. This is the famous Submerged Forest. Standing amongst the stumps of pine, oak and other trees, on a calm evening as the last of the ebb-tide laps about their roots at dusk, one is taken back through the ages to the time when this now ghostly forest once flourished.

The wood is not fossilised as such: it looks and feels just like what one might expect waterworn wood to look and feel like. The peat is hard and compact. Above it, there lies a layer of bluish-grey clay and, at the south end of the beach, atop the clay is a second, thinner peat. The succession records the transition, due to rising sea-levels, from forest to salt-marsh, between about 6,500 and 3,000 years ago.

This period marks the waning stage of the rapid global sea-level rise of approximately 120 metres that accompanied the deglaciation that set in following the last Glacial Maximum, some 20,000 years ago. For the people of Borth, then, sea-level rise is nothing new: that they have the remains of a forest that becomes visible at low tide is evidence enough for them. One of the objectives of the recently-opened sea-defences scheme is to buy time in the face of current sea-level rise, small on a per annum basis but over decades it is easy to see the cumulative risk.

In February 2012, Dr Denis Bates, who was one of my lecturers as a geology undergraduate at Aberystwyth too many years ago to admit, noticed that a new area of ancient peat had become visible along the southernmost part of the beach. With the natural curiosity that is inherent in so many geologists, he took a closer look and made an interesting discovery: the peat contained scatters of burnt stone.

Burnt stone - often forming mounds - is an archaeological feature typical of Bronze-Age sites. It consists of sharp, angular fragments of bleached-looking rock. For an as yet not precisely-known reason, the people back then would heat hefty-sized pebbles in fires and then dunk them into containers of water, the instant cooling shattering them. Perhaps it was a way of producing hot water: some people have even suggested that the process had something to do with sweat-lodges!

Martin Bates, Denis' son, is an archaeologist based at the University of Wales, Lampeter, and his interest was immediately sparked, for very little of antiquarian interest had previously been found at the Submerged Forest: an Aurochs skeleton, discovered many years ago, and a couple of reported flints being about it to date. But on commencing an archaeological survey of the site, what he and his team found was a whole lot more than they expected.

Upon the surface of the upper peat layer, and impacting into the clay below, were footprints. Not just animal either: there were human prints. I visited the site with Martin on a recent morning over low tide and we examined the circular depressions made by the hooves of cattle and sheep; not only did we examine the known human prints but we found a superb new one where sand had been newly scoured away, exposing the hidden peat below. It appears that the adults were foot-clad, but one print, belonging to a child aged, it is thought, about four years, showed the impressions of bare toes. Standing next to such impressions, my heavy rigger-boots now hardly leaving a mark on the surface, Martin explained to me how the environment would have looked at the time that these people were there. It would have been rather like the wide hinterland of the present-day Dyfi Estuary, where acres of salt-marsh are dissected by winding creeks floored by soft mud, giving way landward to patches of boggy woodland. The coast would have been some distance to the north and west, separated from the marsh, just as at the present day, by a barrierlike shingle-spit and sand-dunes. Over time, as sea-levels rose, the whole system advanced landwards: storm-beach, dunes and marshes alike.

 This find represents the first documented evidence of human habitation from the submerged forests of the Mid-Wales coast, though just inland, where low, oak-clustered rocky hills rise from the marshes, there are  metal-mines, the oldest parts of which date back to a similar period - the Bronze Age. The veins of ore that traverse the rocks hereabouts are locally rich in copper - a key ingredient of bronze.

One of the most interesting Welsh Legends is that of Cantre'r Gwaelod - the 'lost hundred'. It refers to a wide and fertile plain that is now lost beneath the waters of Cardigan Bay: it is Wales' version of the Flood Legend which seems to pop up all over the place. Much of this central section of Cardigan Bay is less than 10m deep and the 20m submarine contour is a fair run from ports such as Aberystwyth. A look at sea-level rise data-plots indicates that the final 20m of the post-glacial 120m rise took part during the last 8,500 years or so, most of that occurring during the first thousand years and then slowing markedly. By the Bronze Age, farming and mining were established practices and the rise of the sea was slower, but still ongoing and noticeable. All of that land was certainly lost whilst humans were present in the area. It makes one wonder if a folk-memory did indeed retain a record of drastic geographical change within the time of Man.

Such is the stuff of contemplation. So stand there, on the deserted beach, as on the last of the ebb the waves lap the tree-trunks and stumps and the light falls on a winter evening: lonely calls of oystercatchers echo from shingle to sky and the stars peep out one by one overhead as the dynamic Earth completes another turn.

2012-03-20 02:12:44
John Mason


OK, Grauniad not interested in it, but shall extensively rework!

Cheers - John

2012-03-20 11:10:54


John: I wonder if the burnt stone is related to the heat treated stone discovered at Pinnacle Point, Mossel Bay, South Africa.



The Grauniad's loss is SkS's gain!  :-)

2012-03-21 23:17:07Blog-post drafted
John Mason



A draft blog-post to look at & comment upon is here: http://www.skepticalscience.com/the-forest-beneath-the-sea.html

Cheers - John