Picture: a swampy area in Prince William County, about 20 miles from the site in this story.
The following video from CS&A explains landslides and mudflow, but in Tennessee. Many times these hazards are not covered by insurance and cannot be bought, even with federally-endorsed flood policies. (The only company selling it in TN was "Ace".)
Update: Oct. 20
WJLA reports the release of county funds for repairs to the hillside, has more pictures. Two homeowners had USAA insurance which did not cover this. It is viewed as similar to a flood. Link.