Which factor commonly causes floods in the western United States?

Which factor commonly causes floods in the western United States?

• A. Snowmelt and storms
• B. Tidal waves
• C. Coastal storms
• D. Volcanic eruptions

Answer: (A)

The main idea is that floods in the western United States are most often produced by rapid runoff from snowpack combined with heavy storms. In mountainous regions, large amounts of snow accumulate over winter. When temperatures rise, that snow can melt quickly, and if a storm brings a lot of rain at the same time, the resulting runoff overwhelms rivers and streams. The water spills over banks and floods valleys and towns downstream. This combination—snowmelt plus storms—is why spring floods are so common in the West. Tidal waves (tsunamis) aren’t a regular flood source for this region, and while coastal storms can cause flooding along the coast, they don’t explain the typical inland flood events seen across western basins. Volcanic eruptions can cause local floods through ash, lava, or lahars, but they’re not the usual widespread cause of floods in the western United States.

The main idea is that floods in the western United States are most often produced by rapid runoff from snowpack combined with heavy storms. In mountainous regions, large amounts of snow accumulate over winter. When temperatures rise, that snow can melt quickly, and if a storm brings a lot of rain at the same time, the resulting runoff overwhelms rivers and streams. The water spills over banks and floods valleys and towns downstream. This combination—snowmelt plus storms—is why spring floods are so common in the West.

Tidal waves (tsunamis) aren’t a regular flood source for this region, and while coastal storms can cause flooding along the coast, they don’t explain the typical inland flood events seen across western basins. Volcanic eruptions can cause local floods through ash, lava, or lahars, but they’re not the usual widespread cause of floods in the western United States.