Flash floods are danger in the canyon country of the American Southwest, and in many other regions of the world. The recent tragedy of hikers swept to their deaths reminded us that hikers are particularly vulnerable to flash floods, especially when hiking in narrow slot canyons with no way out.

The Los Angeles Times published a particularly moving and thoughtful story: Seven Hikers Descent into Doom in Zion National Park

After the recent flash floods in Utah, a Search and Rescue Team looks for victims. (photo AP/Michael Chow)
After the recent flash floods in Utah, a Search and Rescue Team looks for victims. (photo AP/Michael Chow)

When a thunderstorm breaks over the mountains and desert, rain falls fast and furious. These rains—calling them torrential is not overstating their severity—quickly spill into gullies, arroyos and canyons, dislodging and carrying along boulders, trees and massive amounts of mud. Animals—and occasionally people—can be trapped or surprised by a flash flood cascading down what was dry passageway just a short time earlier.

Flash Flood Precautions

• Keep an eye on the sky. Watch for storm cloud patterns. Listen for thunders.

• If a storm is approaching, avoid slot canyons and other narrow canyons and gulches.

• Check weather reports frequently, particularly on the morning of your hike.

• Backpackers should camp on high ground, but avoid the crests of ridges or peaks.

Your classic cumulonimbus, or threatening cloud is not a subtle presence in the skies over the Colorado Plateau. When it’s right over you, it appears dark and ominous, and often assumes the shape of an anvil.

Visitors Beware: Flash floods occur even in Death Valley NP.
Visitors Beware: Flash floods occur even in Death Valley NP.

While it’s easy for the hiker to make a thunderstorm ID when one of those nasty looking clouds looms overhead, the same storm cloud may look white and bright when observed from farther away. Since flash floods can roil down a canyon as a result of a storm unleashing a deluge on a mountain located many miles away, a thunderstorm need not occur directly overhead to pose a danger to hikers.

Flash floods, at least in the American Southwest where they are most notorious, can occur from isolated thunderstorms at any time, but there is a distinct “Flash Flood Season” that extends from early summer to early autumn.