The 1925 Santa Barbara Earthquake: The Dam Break
The Sheffield Dam, located at the base of the Santa Ynez Mountains at the northern end of Santa Barbara, has the distinction of being the only dam in the United States to fail during an earthquake. It was built in the winter of 1917, was 720 feet long, 25 feet high, and, at the time of the earthquake, held 30 million gallons of water.
The dam was built on sandy soil--always a danger in an earthquake. The earthquake caused the pore fluid pressure in the soil to jump dramatically, making the soil act more like a liquid than a solid. This phenomenon is known as liquefaction. The center of the dam, about 300 feet of it, simply floated away on the liquefied soil, traveling about 100 feet downstream.
The dam was located quite close to the city, and a wall of water rushed between Voluntario and Alisos Streets, carrying trees, automobiles, and three houses with it, and leaving behind it a muddy, debris-strewn mess. The water filled the lower part of town up to two feet deep, until it gradually drained away into the sea.