Mudflows Devastate Parts of Southern California

Sediment from January mudflows burying cars and homes in Montecito, California, seen on January 10, 2018. California National Guard/Flickr. This week has been a tragic one for parts of Southern California. Heavy rains have triggered landslides and mudflows that have killed over 17 people with dozens more missing. Now, this tragedy is a sequel to an earlier disaster: Wildfires ravaged the coastal mountains near Santa Barbara. However, they are two events that tend to go together because the effects of one prompt the other. The wildfires that burned forests and homes in 2017 have the net impact of destabilizing rugged terrain like is found in towns like Montecito, where numerous mudflows have struck. As vegetation is burned - both trees and ground plants - the soil is exposed to rain water (or snow melt, in other places). The soil absorbs the water, but instead of having plant roots to keep much of that soil in place, it becomes a slurry that's vulnerable to the force of gravity. The material can move downhill into stream and river channels. It can also cause whole hillsides to become unstable and create landslides that move debris into valleys and, again, into rivers and streams. They can occur with little-to-no warning after rainstorms, so getting people out of their path is challenging (more on that below).