By Sid Perkins
An unexpectedly large canyon carved by a Texas flood may help scientists estimate the size of ancient megafloods believed to have sculpted terrain on both Earth and Mars, new research suggests.
![](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2010/06/12629.jpg?resize=300%2C225&ssl=1)
![](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2010/06/12638.jpg?resize=300%2C195&ssl=1)
The new canyon has many characteristics similar to those presumed to have been sculpted by larger-scale floods in other terrains, including streamlined features like ones that appear in images taken by Mars-orbiting probes, says Caltech geologist Michael P. Lamb.
In July 2002, record flooding in central Texas caused Canyon Lake, a reservoir held behind a dam about 55 kilometers northeast of San Antonio, to overflow. Water rushing through the dam’s emergency spillway carved a 2.2-kilometer-long canyon downstream of the spillway in just three days, Lamb and colleague Mark Fonstad, a hydrologist at Texas State University in San Marcos, report online June 20 in Nature Geoscience.