1. Ainthorpe Landslide North York Moors Yorkshire March 5 th 1999 Louise Procter Alison Pepper

2. What Happened? A very wet winter in 1998/9 Heavy rain in the week prior to landslide A step in the road of 100mm was found a day or two before March 5 th Step continued to grow over the next few days to a total height of 1m

3. Subsidiary slumps within main soil mass created head scarps and small grabens which break up the road tarmac

4. Site Geology Western Slope of the Coombs Formed within Jurassic Strata –Made up of shale and interbedded sandstone Ground dips to the North –Valley elevation from 240m to 400m Surface material is weathered –Low heather, bilberry and bracken on the top of the moor –Grass at the bottom of the valley, previous pasture land –Glacial till on valley floor

5. Timeline of Events 1889 and 1929 –Previous landslides formed steps of 250mm; –After 1929 landslip, a ditch was dug by hand across the moor 1980 –Motorbike trials on the moors damaged vegetation cover 1989 –Bracken reduced

6. 14 th Nov 1993 –Heavy rain led to flooding of culvert Dec 1993 –Second ditch dug to divert surface flow 5 th March 1999 –100mm step in road –Increased over few days to 1m –Movement ceased after a week Summer 1999 –Heavy rain could have caused a second slide

7. Possible Prevention Measures 1Improve and extend existing ditches to take water North of landslide area → Favoured option 2Interceptor drains 300mm below the surface 3Discard and block all ditches & enlarge culvert 4Increase plant cover to retain water in the soil