The storm that hit California’s coast between Jan. 26 and 28, 2021, blew out a portion of Hwy 1 near Big Sur. On Saturday, a USGS reconnaissance flight snapped this dramatic photo above the Rat Creek drainage showing the debris flow.

Photos, like the ones in this GIF taken of the same location, are used to monitor coastal change over time. Photos are used by USGS and partner researchers who use data to inform a variety of studies and products, including USGS hazard assessments. https://landslides.usgs.gov/hazards/postfire_debrisflow/detail.php?objectid=297

USGS-produced hazard maps of the denuded, burned hillsides around Big Sur, California, are critical for planning and emergency agencies, like @NWS, to help save lives and property.

The maps help officials identify potentially dangerous conditions, so they can issue warnings and sometimes evacuation orders and close roadways before and during extreme weather events like the one that hit on January 27, 2021.

The USGS landslide team monitors and continue to update the hazard map models based on data collected in burn areas. This information improves future models and provides better hazard assessments used by officials for emergency response and decision making.

Many of the steep hillsides burned and denuded in California fires repel water rather than soak it in.

This condition, called hydrophobic soil and caused by the fire’s hot temperatures, causes water to flow over land instead of soaking in, picking up surface debris along the way with potentially devastating force once it reaches people, communities or property.

USGS collects data about the contaminants found in water flowing off the burned areas. To do this, geochemists collect sediment samples right after a fire, before the rain, and periodically return for additional sampling to understand how contaminants move through the ecosystem.