The Submerged Landscape of Scapa Flow
The landscape of Orkney has changed considerably since the end of the last Ice Age some 11,000 years ago. Despite a drop in relative sea-level of up to 40m, the depth of the Pentland Firth means that Orkney has always been an island, but when the glaciers first retreated, it comprised a single island with a large landlocked bay to the south, where Scapa Flow lies today. Since then sea-level has been rising; recent dates obtained by the Rising Tide project indicate that present day sea-levels were only reached around 4000 years ago, and a very slow increase is still taking place.
This means that when people first came to Orkney in the millennia after the Ice Age they would have found a much larger landmass, and since then the inhabitants of Orkney have had to cope with a process of dynamic environmental change as the sea rose and the coasts retreated. The early inhabitants of Orkney were no strangers to sea-level rise.
These first settlers were hunters and fishers, they are known today as Mesolithic. The coast provided abundant resources and many of their settlement sites lie around the coasts of Scotland. Scapa Flow would have been important to them: a source of fish, shellfish, sea birds and mammals as well as coastal vegetation, all of which they could have made use of. In general, evidence for the Mesolithic settlement of Scotland has been lacking in Orkney, but a quick glance at the map to the right shows how much of the coastal land that they favoured is now submerged below the shallow Orkney seas. It is possible that in some places the evidence of their passing still lies buried beneath the sediment that has accumulated as the seas rose.
In places, the submerged coastal lands of Orkney also preserve buried evidence of the environment in the centuries before the seas rose. Deposits of peat survive in the inter tidal zones of many beaches, witness to a time when the vegetation of the coastal lands comprised patches of marsh and bog land. Elsewhere actual tree trunks survive, relicts of coastal woodland that must have grown above the shore. The study of these remains can provide important evidence, not just of the people of the past, but also of the world that they inhabited, a world that was, in many ways, very unlike our own.
The work of the project
This project seeks to examine evidence from two locations towards the ancient mouth of Scapa Flow in order to cast light on this ancient world.
To the east, at the Sands of Wright, lies a small lochan known as the Dam of Hoxa. Sediments from this lochan will be analysed in order to provide evidence of the rising sea levels and increasing salination of the lochan as the sea approached. Microfossils from the loch sediments provide evidence of this change which can then be dated. In addition, local evidence of submerged tree trunks which emerge from the Sand of Wright at extreme low tides, will be checked, and if possible samples taken for analysis and dating.
To the west the sheltered waters of Mill Bay on Hoy, just to the north of Lyness have been found to contain evidence of submerged peat along the shore. Thiswill be sampled, analysed and dated. Mill Bay was the subject of some interesting aerial photographs taken in the autumn of 2009 by the Royal Commission on the Ancient and Historic Monuments of Scotland. These show considerable evidence of human activity on the seabed in the bay. It is likely that most of this evidence relates to the period during and between the wars when Mill Bay was used, among other things, for the salvage and breakage of the vessels of the German High Seas Fleet. But some features, such as a fish trap on the western shore, may well be much earlier. Work in Mill Bay obviously holds considerable potential.
The dates obtained from sediment analysis will be used to provide further evidence for the height of the past sea-level at specific times. They can be added to the information already obtained elsewhere in Orkney by the Rising Tide Project in order to build an overall picture of the changes in sea-level that have taken place since people first came to Orkney. Work in 2010 will concentrate on taking samples and preliminary analysis.
Text courtesy of Caroline Wickham-Jones