Which hazard poses a greater threat if you live about 30 miles from a stratovolcano?

Which hazard poses a greater threat if you live about 30 miles from a stratovolcano?

• A. Lava flows
• B. Ash fall
• C. Lahar
• D. Pyroclastic flows

Answer: (C)

Lahars are volcanic mudflows that form when rain or melted snow mixes with volcanic ash and debris, turning into a fast, heavy slurry that races down river valleys and can keep moving for many kilometers downstream. Because they follow drainage paths, they can reach areas tens of miles away from the volcano, burying rivers, towns, and infrastructure even after the eruption has ceased. Lava flows tend to stay on the volcano’s slopes and move slowly, so they rarely reach distant locations like 30 miles away. Pyroclastic flows are incredibly deadly but are confined to steep, nearby terrain and usually travel only a limited distance from the vent. Ash fall can blanket broad regions, but the combination of rapid downslope movement through waterways makes lahars the greater threat at that distance.

Lahars are volcanic mudflows that form when rain or melted snow mixes with volcanic ash and debris, turning into a fast, heavy slurry that races down river valleys and can keep moving for many kilometers downstream. Because they follow drainage paths, they can reach areas tens of miles away from the volcano, burying rivers, towns, and infrastructure even after the eruption has ceased. Lava flows tend to stay on the volcano’s slopes and move slowly, so they rarely reach distant locations like 30 miles away. Pyroclastic flows are incredibly deadly but are confined to steep, nearby terrain and usually travel only a limited distance from the vent. Ash fall can blanket broad regions, but the combination of rapid downslope movement through waterways makes lahars the greater threat at that distance.