The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
In Moon Township in Pennsylvania, a landslide has forced two families to vacate their homes. The landslide has occurred above Beaver Grade Road, on the slope that links a comparatively new housing development, known as Sonoma Ridge.
WTAE-TV Pittsburgh has tweeted an image of the site:-
The Google Earth image below includes the affected area:-
The location of the landslide is [40.4696, -80.1608]. Archive Google Earth images might hint at what lies behind this landslide, although a proper investigation is needed, of course. This is an image of the site from 1993, before the houses had been constructed:-
The site of the landslide has an interesting morphology, with a steep slope rising up to plateau on which the houses were ultimately constructed. I wonder if material was cut from this area to provide fill for other sections of the road?
An image of the site in 2007 shows the early stages of construction of the Sonoma Ridge development:-
What is notable here is that a large amount of fill appears to have been emplaced to create the platform for the houses. Note the apparent thickness of the fill in the lower right portion of the image.
It appears on first inspection that this fill slope might be involved in the failure. Again, I would would emphasise that this is speculation, and that a proper investigation is needed, but I would be interested in seeing the design for these fill slopes, and the measures that were put in place to manage their stability, if I were undertaking an investigation at this site.
It seems unlikely that the home owners are in any way to blame for this issue. However, as a family in Alaska has just discovered, most household insurance policies do not cover landslides in the USA (or in the UK, incidentally). Once again, this has created a nightmare situation for those affected.