Huge Crack at Edwards Healing

A huge crack in the earth at Edwards Air Force Base that two years ago forced the temporary closure of a dry lake bed runway is healing, thanks to two wet winters that have filled the normally dry lake and washed soil and silt into the opening.

The crack, situated on the southeast end of Rogers Dry Lake only about five miles from another runway used by space shuttles, was discovered in January, 1991. At that time, it was about three-quarters of a mile long, as deep as 14 feet and as much as six feet wide. A hydrologist with the United States Geological Survey said it was probably the largest fissure ever discovered in California.

Now the fissure’s deepest points are at a comparatively shallow three feet with most of the opening only about 12 inches deep, according to Mel Marmet, airfield manager at the sprawling military base.

Cracks are not new in the mostly clay surface of the 45-square-mile Rogers dry lake bed, which contains 16 runways and is the larger of two dry lake beds on the base. But none have been close in size to the one that opened in early 1991, Marmet said. In fact, another fissure opened last winter near the large one. It’s the second-largest crack found on the base, measuring nearly one-third of a mile long with a depth of one foot or less.

An ongoing study at Edwards AFB by the U.S. Geological Survey found the fissuring was caused by land subsidence, the result of over-pumping of ground water. The USGS found that portions of Edwards AFB have dropped as much as 3.3 feet since 1961 because of the removal of water from beneath the desert base.

Concerns about the damaging effects of that excessive pumping in large part prompted Edwards AFB officials to partially switch the base’s water supply from local wells to the California Aqueduct.

Until March, the air base relied solely on ground water to supply the needs of the 15,000 people who work there and the thousands who live on the base. A $1.2-million pipeline allowed the military to begin using imported water along with the well water. The base receives about 1.5 million gallons a day through the pipeline, which is capable of delivering nearly twice that amount.

James Blodgett, a hydraulic engineer and former project manager on the 5-year, $5-million USGS study under way at the military base, said reducing the amount of ground-water pumping should result in less fissuring of the Edwards runway lake beds.

“We’re working with a dynamic situation here,” he said. “Until the original problem (of excessive ground-water pumping) is eliminated you’re always going to have this problem of fissuring.”

Blodgett said that as Edwards AFB pumped water from the underground aquifer, air filled the void once occupied by water, and the area eventually collapsed under the weight of the clay soil, opening fissures.

Blodgett said although the huge fissure at Edwards AFB is becoming filled in by the weathering process, the area will never be as strong as it once was.

It will not, however, affect the military’s ability to use the lake bed runways, Blodgett said.

In fact, Marmet said that after the fissure opened in early 1991 it took crews about six months to fill in the portion of the crack that crossed the lake bed runway, which has been in use since.

The rest of the fissure began to show signs of healing naturally after the 1991-92 winter rains, Marmet said. Although the width of the crack grew to 14 feet as its edges collapsed, its maximum depth was only six 6 feet.

As he put it: “Mother Nature works for us and against us at times.”