California Institute of Technology - 20 June 2010
Modelling Mars in a Texan torrentIn the summer of 2002, a week of heavy rains in Central Texas caused Canyon Lake—the reservoir of the Canyon Dam—to flood over its spillway and down the Guadalupe River Valley in a planned diversion to save the dam from catastrophic failure. The flood, which continued for six weeks, stripped the valley of mesquite, oak trees, and soil; destroyed a bridge; and plucked meter-wide boulders from the ground. And, in a remarkable demonstration of the power of raging waters, the flood excavated a 2.2-kilometer-long, 7-meter-deep canyon in the bedrock.
Eroded gorge. (Michael Lamb/Caltech)
Streamlined islands sculpted by the flood and large boulders
transported by the flood. (Michael Lamb/Caltech)
According to a new analysis of the flood and its aftermath ... the canyon formed in just three days.
The analysis revealed that the rate of the canyon erosion was so rapid that it was limited only by the amount of sediment the floodwaters could carry. This is in contrast to models normally applied to rivers where the erosion is limited by the rate at which the underlying rock breaks and is abraded.
The abrasion of rock by sediment-loaded waters—while less significant in terms of the overall formation of the canyon—produced other features, like sculpted walls, plunge pools at the bases of the waterfalls, and teardrop-shaped sediment islands.
The results, Lamb says, offer useful insight into ancient megafloods, both on Earth and on Mars, and the deep canyons they left behind.
Nature News - 20 June 2010
Rapid formation of a modern bedrock canyon by a single flood eventA torrential downpour that carved a seven-metre-deep canyon through the Texan landscape in just a few days is providing valuable insight into the processes that shaped the surface of Mars.
Erosion is usually a slow process, but occasionally rivers rise up in mammoth floods that cut new channels practically overnight.
Some of the biggest and best-studied of these events are thought to have occurred on Mars, and in North America at the end of the last Ice Age, when the Missoula Floods carved the 'Channeled Scablands' of Washington State. All of these occurred long before anyone was around to witness them, leaving scientists with only models of erosion to fall back on.
But in 2002, almost one metre of rain fell on the Texas hill country north of San Antonio in the course of a week. This caused a reservoir on the Guadalupe River to overflow, sending water crashing down an emergency spillway and into a narrow canyon that had previously carried only a small stream.
The flow rate topped 1,450 cubic metres per second. After five days, the new river had ripped a gorge of up to 7 metres deep and up to 12 metres wide into the limestone bedrock.
The study goes some way towards verifying the mathematical models used for describing the erosional rates of ancient megafloods. But those floods were much larger than that studied by Lamb and Fonstad, leading to some doubts about how generalizable the Texas findings are.
- Nature Geoscience | 20 June 2010 | doi: 10.1038/ngeo894
Science News | 20 June 2010
Data Deluge: Texas Flood Canyon Offers Test of Hydrology Theories for Earth and MarsFlood carved surprisingly large gorge that may help understand features on Earth and Mars.
Scientific American | 21 June 2010
A 2002 Texas megaflood carved a 2.2km canyon in three daysA massive overflow from a dam in 2002 carved a channel several meters deep into the bedrock in just days.
ars technica | Nobel Intent | 21 June 2010
Most of the dramatic features of river basins—canyons, gorges, and so on—formed through rather mundane processes, primarily the slow erosion caused by a constant flow of water and seasonal floods. But researchers have also identified a few cases, both on Earth and Mars, where features seem to have been formed by sudden massive flooding (on Earth, these are often associated with glacial melting). We have geological evidence of these catastrophic events, and models that reproduce their behavior but, because they're extremely rare, it has been impossible to test how well these models do when compared to a real event. Scientists have now identified a Texas flood that carved a seven meter deep canyon in 2002 that presents just such a rare opportunity.