San Gabriel Valley areas scarred by the Eaton Fire are at “high to very high risk” of debris flows this week. How do they happen? What is being done to prepare? And what do survivors of a catastrophic one that killed 23 people remember about the day that the hills came down?

In the Los Angeles area, the burn scars that carry the highest risk are those from the Eaton and Palisades fires from January and the Bridge Fire from the fall.

A powerful storm moved through the Los Angeles region Thursday, flooding streets, prompting evacuation warnings, and threatening mudslides in fire-ravaged areas. By Thursday evening, a debris flow had closed Mulholland Drive,