As I write this, northern California is experiencing the second straight week of rain in an otherwise very wet year. Continuous rain soaks the ground and loosens unstable hillsides. Landslides can stay hidden for years until very wet weather suddenly breaks them loose. Also, slides can move very slowly, over long periods of time, gradually damaging the properties around them.
In either case, earth movement can cause serious damage to buildings and other improvements on or adjacent to the unstable land. Mudslides, rockslides, and landslides are all versions of the same phenomenon—water plus gravity equals damage.
We’ve seen slides gradually pull down the surrounding properties so slowly that trees growing on the hill have curved trunks. This is called soil creep and can last for years or decades. We’ve also represented clients whose homes were damaged in just a moment as a large landslide, hidden beneath the surface of the earth for centuries, comes down, bringing a large portion of the hillside with it.
Property developers are required to obtain the advice of soil engineers when grading is done in a landslide-prone area, and most engineers are very good at detecting the presence of hidden slides. Aerial photo mapping, boring, or just reviewing the history of the area under development can do this. But regardless of the engineer or developer’s efforts, slides can still occur.