The Landslide Problem

Steep hillsides can not only lead to flash floods, but also to landslides and mud slides. This is particularly the case after deforestation, or where the soil is unstable, sandy or peaty. The worst British landslip in recent times was in 1966 at the Welsh village of Aberfan . 116 children and 28 adults were killed after heavy rain caused waste from a coal tip to slide onto a school.

Peat slides are a particular problem after a period of dry weather. The peat dries out, and becomes like a sponge. A heavy rainstorm then soaks through the peat to the ground beneath, where it acts as a lubricant, making the ground unstable.

Landslides seem to be becoming more common, due mainly to reduced rainfall in summer months, combined with more severe short duration rainfall events associated with thunder storms. For example:

Shetland, 19th September, 2003

The summer of 2003 was a very dry one for Shetland. The winter and summer the year before had been dry too. For the first time in living memory, drinking water had to be imported in bulk to some of the outlying islands by ships from the mainland. In September 2003, however the weather broke, and torrential rain fell, just to the south of Lerwick. This caused a series of dramatic peat slides all morning which destroyed or damaged five miles of the A970 main road. A bridge collapsed in the southern part of the main island, and a newly installed water main to the south of the island was breached, along with several sewage pipes.

Although the area is relatively remote, several cottages and farm buildings were destroyed, along with a number of sheep which were washed into the sea, but fortunately no human lives were lost.

If the rain had fallen just a few miles further north, the outskirts of the town of Lerwick could have been devastated, as it is surrounded by peat covered hills. Fortunately where the rain fell the exposure was low due to the remoteness of the area, and the vulnerability was low as the slips happened in daylight hours.

On the same night in Ireland , there were 40 slides recorded in County Mayo , followed a month later by another massive peat slide in County Galway .

This section is based on an information bulletin from Shetland Islands Council and several contemporary reports in "The Shetland Times", and "Shetland Today"  Prince Alfred Street , Lerwick, Shetland , UK , ZE1 0EP

Perthshire, August 2004

Perthshire suffered from two major landslide events in 2004, fortunately again no lives were lost but there was considerable disruption. First, heavy rain caused a sand gravel and mud landslide which blocked the A9, the main trunk road from Inverness to the south, then the following week another heavy rainstorm, associated with the biggest electrical storm on record in Scotland, resulted in two landslides in Glen Ogle near Lochearnhead, trapping 20 vehicles on the A85 including a bus. 57 people had to be airlifted by helicopter from the scene. Again it was fortunate that the slips happened in daylight hours and that no buildings were affected. Glen Ogle was the site of two previous landslides in 1965 when the railway line was blocked, resulting in the permanent closure of the line.

Mapping

The British Geological Survey has produced a map showing that large areas of the country are at moderate or significant risk of landslides. They have been quoted as saying "The past few years do seem to have had an increase in landslide activity over the country as a whole. If the forecasts of the climate change experts are correct, we are likely to get more frequent, intense rainfall. That can cause more of the kind of landslides we've seen."

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