Download - Ainthorpe Landslide North York Moors Yorkshire March 5 th 1999 Louise Procter Alison Pepper
Ainthorpe LandslideNorth York Moors
YorkshireMarch 5th 1999
Louise ProcterAlison Pepper
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 5th
• Step continued to grow over the next few days to a total height of 1m
Subsidiary slumps within main soil mass created head scarps and small grabens which break up the road tarmac
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
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
• 14th Nov 1993– Heavy rain led to
flooding of culvert
• Dec 1993– Second ditch dug to
divert surface flow
• 5th 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
Possible Prevention Measures
1 Improve and extend existing ditches to take water North of landslide area
→Favoured option
2 Interceptor drains 300mm below the surface
3 Discard and block all ditches & enlarge culvert
4 Increase plant cover to retain water in the soil