Dangerous flash flooding occurs as an arroyo becomes filled with water in Carson Valley, Nevada, on July 20, 2014. (YouTube Video/John T. Humphrey)
Arroyos, the Spanish name for streams, are gullies located in the southwest United States that develop during severe rain storms. Washes, another name for arroyos, are dry most of the time, but when a storm comes through, they help to drain excess amounts of water to local streams or rivers, according to Senior Meteorologist Jim Andrews.
"It is no different than asking how the Mississippi River formed," Andrews said.
These rivets in the desert landscape may only come to life with excessive amounts of water during a storm that produce an extreme amount of wet weather, usually every 100 years or so. The arroyos, described as little fingers in the landscape by Andrews, are bare to the elements. Once the fast-flowing rain water is transported in the arroyos, the ground wears down even more. An arroyo can be described as an intermittent stream, meaning it flows only part of the time when it rains.
The arroyos can cause a flash flood in areas that have not received any rainfall. Andrews suggests not camping or putting anything you don't want washed away in an arroyo. Sometimes the water that is rushing through an arroyo may move through different locations. The summer months are the most dangerous for arroyos, because of the severe summer thunderstorms that are produced in the desert.
Story by AccuWeather.com Staff Writer, Molly Cochran.
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