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