Lahar

volcano · natural disaster · mudflow · extreme geology

Made from volcano stuff. Lahars are mixtures of pyroclastic material (hot ash and rock from eruptions), cold rocky debris, and water all blended together into a thick, dangerous sludge that races downhill.

Faster than you'd think. These mudflows can move incredibly fast, flowing down volcano slopes and river valleys like a giant wave of wet concrete, sweeping away everything in their path.

Water is the key. Lahars need water to form, which can come from melted snow and ice on the volcano, heavy rain, or water from lakes and rivers nearby.

Follows the valleys. Instead of spreading out everywhere, lahars follow river valleys and stream channels like water going down a drain, which makes them especially dangerous to places built in those valleys.

Happens without eruptions. You don't even need an active eruption to get a lahar, because heavy rain can wash loose volcanic material down a volcano's slopes anytime after an eruption.