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 factor behind floods in the western United States is the release of stored water from mountain snowpack, especially when warm spring temperatures arrive and melt the snow rapidly, often combined with spring storms. The West holds a lot of water as snow in the Sierra Nevada, Cascades, and Rocky Mountains. When temperatures rise, that snow turns to meltwater and rushes into rivers. If heavy rain falls during this melt or rain falls on top of snow, runoff increases even more, overwhelming river banks and causing floods downstream. This pattern is typical for western basins feeding rivers like the Columbia, Sacramento, Willamette, and Colorado.

Tidal waves and coastal storms mainly affect coastlines and don’t account for the inland flood patterns most common in the West. Volcanic eruptions can trigger floods locally near volcanic areas, but they’re rare and not the widespread flood driver for the region.