30 November 2012

Multiple landslides in the UK in the last week

Posted by Dave Petley

The exceptional rainfall event in the UK (there is a fantastic gallery of images of the floods at the bottom of this page) about which I blogged yesterday has been responsible for triggering landslides across the country.  Indeed, I have never known so many landslides to occur in the UK – it is a very unusual period.  The highest profile event occurred at Whitby, as covered in my post yesterday, and the news today is that the demolition of the houses has started.

I thought it would be interesting to pull togather a selection of other newsworthy landslides.  There are many more in addition to this set:

1. Landslides on the main railway line in Teignmouth, Devon

The main railway line from London to Cornwall has been repeatedly disrupted by landslides.  This is the same section of line that I featured in my landslides in art series a few weeks ago. The most recent landslide occurred yesterday, and is shown below.  The BBC News website reports that movement has continued and that the site is now being examined by an roped-access team.  The line is not likely to reopen until Saturday.


2. A rockfall in Shropshire

Meanwhile, over in Shropshire the key road into the World Heritage site at Ironbridge has been blocked by a rockfall at Jiggers Bank.  This stretch of road has had repeated rockfall problems and has been subject to a number of remediation exercises, as the image below shows.  The reports suggest that the most recent event was on a section of the slope that had not been engineered.  The road is still closed.


3. Another railway line landslide, this time in West Sussex

Meanwhile, an important commuter railway line suffered a small embankment failure between Holmwood and Dorking, near to Horsham in West Sussex.  Although not large, the landslide shifted ballast from under the sleepers, leaving the track unusable.  This has caused considerable disruption:


4. And yet another railway landslide, this time in Gloucestershire

A very similar landslide to that described above occurred at Westerleigh junction in Gloucestershire, closing one of the two tracks between Bristol and Swindon.  This landslide appears to be larger than the one at Horsham, but has not retrogressed to the point at which the track is undermined.  The article notes that Network Rail, who are responsible for track maintenance, have estimated that the repair will need 4000 tonnes of ballast.


5. A coastal landslide in North Devon

Over in North Devon, a coastal landslide at Saunton occurred on Wednesday night.  This image, captured by Bob Braunton and featured on the North Devon Gazette web site shows the landslide:



So what next?

The heavy rainfall has now moved away, to be replaced by cold weather, so the immediate threat should start to subside.  However, for some slopes the groundwater level will still be rising as the rainfall percolates through, so more landslides are possible.  It is notable though that all of the above landslides are shallow – so far there is not much sign of the deep-seated landslide systems reactivating.  This is almost certainly because groundwater levels were so low after the prolonged drought that ended in the early summer.  These deep groundwater levels will now be rising, so don’t be at all surprised if there are reports of larger landslide movements over the next few months.  Places such as Dorset and the Isle of Wight, where there are large coastal landslide systems, will be particularly vulnerable.  Such landslides represent a comparatively low level of risk to life, but can cause extensive property damage.  It will be an interesting winter.