Flood shows water’s power to recarve land
SAN MARCOS— A year after Mark Fonstad became a geography professor at Texas State University in 2001, he got the chance to do research on something for which no one could have planned.
In the summer of 2002, a flood that reshaped the area’s geological landscape on a scale that normally would have taken thousands of years
happened practically in his backyard.
Massive rainfalls around the July Fourth weekend that year caused a reservoir on the Guadalupe River to overflow. Floodwaters tore through a gorge at the base of Canyon Dam, carrying massive boulders as if they were pebbles, scouring the walls and deepening the valley as they went.
The waters caused $87 million in damage and destroyed or damaged almost 500 homes. They also carved a
Continued from A1 large, picturesque canyon into the landscape.
“This was so huge, it changed everything at once,” Fonstad said.
The data collected by Fonstad and his research partner, Michael Lamb of the California Institute of Technology, on the area before, during and after the flood has applications here on Earth — and on Mars.
The research can be used to determine how unstable a river is and whether its waters could erode rock 10 feet deep, information that would be useful in making engineering decisions, such as whether to build a bridge over a “problem river,” Fonstad said.
The researchers also hope their work will offer insight into how the canyons on Mars were formed.
To understand how a Central Texas flood can be tied to the Red Planet’s geography, one must go back to 2002.
Thanks to a wet spring, Canyon Lake — normally at 909 feet — was already full. Then, on June 30, rains swept in from the Gulf and stalled over the Hill Country for five days, dropping up to 45 inches in areas north and west of San Antonio. Localized rainfall combined with runoff from upriver, pushing things over the edge.
When the lake reached 943 feet, the U.S. Army Corps of Engineers opened the flood- Researchers hope their work will offer insight into how Red Planet canyons were formed. gates at Canyon Dam full blast in an attempt to reduce the volume of water heading toward the spillway, the part of the dam that allows controlled overflow and helps prevent water from topping the dam.
Billions of gallons of water spilled forth from the side of the dam and tore into the Guadalupe River.
“It was very dramatic. It went over at very high speeds,” Fonstad said.
The limestone walls of the valley below were very weak, made up of loosely connected blocks, Fonstad said. The floodwaters picked up about 70,000 tons of rock and carried them downstream, carving 70 feet deep into the canyon floor in some places.
The torrent uncovered fossils, ancient shells and freshwater springs.
Fonstad and Lamb compared topographical images to determine how much earth had been washed away below Canyon Dam. Fonstad said that using data collected on the Guadalupe River flood, he and Lamb can estimate the size of floods on Mars and how much rock was involved to create that planet’s many canyons and gorges.
Their research was recently published in the journal Nature Geoscience.
“There was a tremendous amount of water” on Mars, Fonstad said. “It probably wasn’t created by surface rain, but possibly snow melt or groundwater.”
Brian Hynek, an assistant professor of geosciences at the University of Colorado, recently published a study saying that a vast ocean probably covered one-third of the surface of Mars about 3.5 billion years ago.
The quest to find liquid water on Mars, or prove that it once existed, captivates scientists because on Earth, where there is water, there is life. Hynek said tracking water on Mars is key to tracing the possible development of life there.
“Understanding the history of water on Mars is pretty important (to determine) if life is there, or ever was there,” Hynek said.
The study shows how events on Earth can be applied to other worlds, Hynek said. “Modeling the Earth’s catastrophic floods is a great way to look at Mars.”
Floodwaters, which caused $87 million in damage, picked up about 70,000 tons of rock, cutting 70 feet deep into the canyon floor in some places.