The 2002 Texas floods created a 2.2 kilometre-long and 7 metre deep canyon, all within 3 days.
[social_buttons]A week of heavy rains in Central Texas in the summer of 2002 caused Canyon Lake, the reservoir of the Canyon Dam, to flood over its spillway and down the Guadalupe River Valley in what was a planned diversion to save the dam from catastrophic failure.
The flood continued six weeks, and stripped the valley of mesquite, oak trees and soil, destroyed a bridge and tossed metre-wide boulders downstream, as well as creating a canyon 2.2 kilometres long and 7 metres deep in just 3 days.
Catastrophic Floods Cause Canyons
The evidence is being published in the June 20 advance online edition of the journal Nature Geoscience, and sheds light on an environmental process that we have rarely seen in action, but rather only ever seen the results of.
“We know that some big canyons have been cut by large catastrophic flood events during Earth’s history,” says Michael Lamb, assistant professor of geology at the California Institute of Technology (Caltech), who along with Mark Fonstad of Texas State University performed the analysis on the flood and its aftermath.
“There are very few modern examples of megafloods,” Lamb says, “and these events are not normally witnessed, so the process by which such erosion happens is not well understood.” Nevertheless, he adds, “the evidence that is left behind, like boulders and streamlined sediment islands, suggests the presence of fast water”
This is why the Canyon Lake flood and its effect on the landscape is so important. “Here, we know that all of the erosion occurred during the flood,” Lamb says. “Flood waters flowed for several weeks, but the highest discharge—during which the bulk of the erosion took place—was over a period of just three days.”
Canyon Formation 101
The generally held belief has been that canyons – like the Grand Canyon in America’s state of Arizona – were created over a long period of time by slow erosion of waters. There are canyons such as these all over our planet, as well as on Mars.
The rate of erosion was rapid, which seems obvious considering the effect it had on the landscape. However there is more proof of its strength. The Canyon Lake flood was able to move boulders from the sediment they were rooted in and carry them downstream, sometimes creating 10- to 12-metre high waterfalls along the way, channels and terraces.
On top of this there was the more typical abrasion of rock by the sediment-loaded waters, which is what we normally associate floods with. These waters created other features like sculpted walls, plunge pools at the base of the waterfalls and teardrop shaped sediment islands in the middle of the stream.
These latter are especially important as “these are features we see on Earth and on Mars in areas where we think large flow events have occurred,” says Lamb. “It’s nice that here we’re seeing some of the same features that we’ve interpreted elsewhere as evidence of large flow events.”
The results of Lamb and Fonstad’s analysis are important as they offer insights into ancient megafloods on Earth and Mars that might help us broaden our understanding.
“We’re trying to build models of erosion rates so we can go to places like Mars and make quantitative reconstructions of how much water was there, how long it lasted, and how quickly it moved,” Lamb says. In addition, he says, “this is one of a few places where models for canyon formation can be tested because we know the flood conditions under which this canyon formed.”
Source: California Institute of Technology
Image Source: U.S. Army Corps of Engineers Digital Visual Library
