Lack of rain in California has had an unexpected consequence: it has slowed down the movement of the land. In some regions hillsides move gradually, perhaps sliding a metre or so every year, but over the past five years the dry conditions have reduced this movement to a snail’s pace.
The discovery was made by comparing satellite imagery, aerial photographs and on-the-ground measurements from northern California’s Eel river basin. Initially researchers were puzzled to see that the trees and rocks above the slow-moving landslides in the region had barely moved in recent years. But comparing the land movement data with climate records back as far as 1944 revealed that the slow-down was almost certainly linked to the California drought.
In this case rocks and soil have dried out, and there is no longer enough moisture to lubricate the movement of the land. “A question now is how much water will it take, and how long will it take to get water down the depths at the base of these sliding surfaces to reduce the friction and get them to start moving again,” said University of Oregon researcher Joshua Roering, whose findings have been published in Geophysical Research Letters. This summer the team will be collecting more measurements and trying to better understand the plumbing system beneath these slow-moving landslides.
Slow landslips are typical in many parts of the world, causing roads to crack, rails to buckle and houses to subside. The new data from California will help scientists better understand these gradual landscape changes, and the impact that climate change is likely to have.