From PHYS ORGMudslides, or debris flows, can occur when rainfall washes away the buildup of sediment in mountain channels. Roughly equal parts water and sediment, debris flows are strong enough to carry large boulders downhill and threaten communities on or near the mountains. The debris flows in January 2018 that hit Montecito, California, killed 23 people and caused hundreds of millions of dollars in damage. Authorities attributed the mudslides to the wildfires that swept through the area the previous month. Vegetation holds back the sediment in these steep landscapes, but as the vegetation burns during a wildfire, gravity transports the sediment from the hillsides down to the channel in a process called dry sediment loading, said Roman DiBiase, assistant professor of geosciences at Penn State. (more)