A project to survey the prehistoric landscape around the Callanish Stones on the Isle of Lewis in the Outer Hebrides has revealed evidence of other stone circles hidden beneath the peat, including one with evidence of a large lightning strike in its centre.
The main stone circle, known in Gaelic as Tursachan Chalanais, is a significant Neolithic monument consisting of an arrangement of standing stones situated on a ridge above Loch Roag. In the surrounding area, over 15 other sites have been identified that may be ‘satellite’ stone circles to the main Tursachan, labelled Calanais Sites I to XIII. The Calanais Virtual Reconstruction Project, led by the University of St Andrews with Urras nan Tursachan and the University of Bradford, was designed to increase understanding of these features.
The project used several different geophysical techniques, in order to determine their effectiveness in mapping the Neolithic landscapes of Scotland’s Western Isles, much of which has been buried by blanket peat and rising sea levels during the Holocene. The test-site chosen was Calanais Site XI, or Airigh na Beinne Bige, a single standing stone on an exposed rocky outcrop surrounded by blanket peat bog, overlooking the Tursachan.
The geomagnetic survey of Site XI identified 13 anomalies in a circular pattern, c.30m in diameter. One was associated with the existing standing stone, and the other 12 are believed to be buried stones or settings for stones that were part of a circle of megaliths extending from the one stone remaining.
In the middle of the buried stone circle, the survey found evidence for a magnetic feature in a pattern typically associated with large lightning strikes. The clarity of the strike indicates that it occurred prior to the accumulation of the peat, meaning that it must have taken place over c.3,900 years ago, while its size and intensity suggest that it may be the result of multiple high-density strikes, either in a single storm or through multiple events over time.
It is not known whether the lightning strike occurred before or after the construction of the monument. Lightning is usually attracted to large upstanding features and, although there is currently no such feature in this location, it has been suggested that there may have been a tree or large natural rock on this spot, which the stone circle could have been constructed to memorialise. However, even without such a feature, the exposed area with its rocky outcrops would still have been susceptible to lightning strikes, and it is possible that the monument was simply intended to record the natural phenomenon alone.
Despite the uncertainty surrounding the relationship between the stone circle and the lightning strike, the survey has raised interesting questions about the way in which natural events may have influenced the beliefs of the Neolithic people who occupied this landscape. It has also demonstrated that various types of land and marine geophysics can be used successfully to reconstruct the palaeo-landscape, and the team hopes to return this year to conduct further surveys and learn more about Neolithic activity around the Tursachan.
For further details of the project, see http://hdl.handle.net/10023/19121.