Changing climate could lead to more landslides, say scientists

By NEIL RIDDELL

CLIMATE change could make a repeat of the shocking landslides of five years ago more likely, with a number of areas throughout Shetland under potential threat according to a new map from the British Geological Survey (BGS).

Among the locations in the isles which could be under threat are sections of the South and Central Mainland, the Ward of Bressay and the most northerly tip of Unst, including the nature reserve opposite Hermaness and the Saxa Vord hill, while a sizeable chunk of the west side of Foula is also marked as having a “significant” potential for landslides.

Dr Alan Dykes, of the school of earth sciences and geography at Kingston University, told <i>The Shetland Times</i> this week that it was probable climate change would increase the likelihood of landslides like those seen in the South Mainland in September 2003.

He said: “Many of the more damaging incidents in recent years of smaller slide-type peat landslides appear to be associated with ‘extreme’ rainfall (however defined) following dry weather, i.e. heavy rain falling on peat that has dried and consequently cracked the surface.

“Current climate change scenarios for the UK in general show (a) warmer, drier summers and (b) more frequent occurrences of ‘extreme’ rainfall events at any time of year.”

The BGS map gives a broad indication of where landslides are more likely to occur based upon geological conditions at a particular location. But BGS landslide expert Dr Andrew Gibson stressed that viewers should not make “incorrect assumptions about how dangerous a location is” and should instead contact the BGS for more detailed impact assessments of the hazard risk at a given locality.

He said it was hard to say how likely future landslides in Shetland would be. “Unfortunately, it is very difficult to predict the pattern of landslides – where they will occur, or when,” said Dr Gibson. “This would need a detailed understanding of ground conditions and long term patterns of weather. Our understanding of these is improving, but the natural systems we are dealing with are complicated and require further research.”

An academic paper on the nature of the landslides in the South Mainland, by Dr Dykes and Dr Jeff Warburton of Durham University, was published earlier this year.

The landslides then saw sections of a five-mile stretch of the A970 road between Cunningsburgh and Levenwick blocked by huge quantities of mud and rubble, while houses in Sandwick and Hoswick were badly affected by flooding, with some gardens virtually obliterated.

The 20 significant peat slides and 15 smaller landslides were triggered by a night of extreme, prolonged rainfall following a dry summer and preceding winter, which caused some outlying islands to require drinking water to be imported by ship for the first time in decades.

The Dykes and Warburton paper concluded that improved understanding of peat instability “may only be obtained from investigations of the many more such failures that may be predicted to occur in future years”.
SIC head of roads Ian Halcrow said that following the landslides five years ago consultants were commissioned to write a report, which is in the process of being finalised. In the immediate aftermath of the landslides, the roads department terraced the slope above a particularly vulnerable section of the A970 at Channerwick to lessen the chances of a repeat.

He said: “We also did some drainage works at that time to provide positive drainage for water rather than having it building up under the peat and perhaps triggering a landslide. In practice landslides are associated with such extreme rainfall that it’s not something that’s terribly predictable.”

Mr Halcrow admitted that future changes in weather patterns because of climate change were of concern “across the board”.

He added: “We did identify an area above the Dale golf course at the Lerwick side of the valley that was causing us a bit of concern and, in agreement with the landowner we did some drainage ditches in a field there. We’ve tried to be aware and keep an eye on things.”

Featured above is the low resolution map of areas of instability and potential landslides for Shetland. More detail is available from the BGS which will provide information on request at a “relatively low cost” in the form of a ground stability GeoReport. Anyone who wants more information can visit the BGS website at http://shops.bgs.ac.uk/georeports/example.cfm?type=HS.