Heavy rains make Southern California vulnerable to flooding and debris flows, especially after fires that strip steep hillsides of vegetation.

Mudflows, mudslides and landslides often are used interchangeably when disaster strikes, but the terms have distinctions.

A mudflow is “a river of liquid and flowing mud on the surfaces of normally dry land areas,” according to the Federal Emergency Management Agency.

“Other earth movements, such as landslide, slope failure or a saturated soil mass moving by liquidity down a slope, are not mudflows,” it says.

FEMA sees a mudflow as similar to a milkshake, while the more solid mudslide is comparable to a cake.

The US Geological Survey dismisses mudslide as an “imprecise but popular term … frequently used by laymen and the news media to describe a wide scope of events, ranging from debris-laden floods to landslides.”

A landslide occurs when soil or rock moves downhill, usually due to gravity, but erosion, heavy rains and earthquakes can contribute to landslides.

Sources: FEMA, US Geological Survey