Erosion may not always be a slow and steady process, according to a recent study by the University of Colorado, Boulder. Instead, the earth can degrade and crumble suddenly due to extreme weather events such as the September 2013 storm, which triggered widespread flooding across Colorado's Front Range. This historic storm did the damage of hundreds or even one thousand years in accumulating sediment from Boulder's west foothills, according to their research.
"In Boulder Canyon and similar areas, the majority of the sediment transfer down slopes occurs during these rare, punctuated events following hundreds of years of weathering to produce the sediment," Suzanne Anderson, a research fellow at the Institute for Alpine and Arctic Research (INSTAAR) and co-author of the new study, said in a statement. "The 2013 storm was a unique opportunity to catch the sediment movement in action."
When conducting their study, researchers used high-resolution topographic maps generated using LiDAR (Light Detection and Ranging, a laser technology), to make their measurements. According to the release, they compared LiDAR data collected by the Federal Emergency Management Agency (FEMA) in November of 2013, to a dataset collected in 2010 by the Boulder Creek Critical Zone Observatory.
"The long-term erosion rate in this area is about two tenths of an inch per century--that is less than the thickness of a human hair per year," Anderson explained in the release. "It took a large storm to mobilize accumulated sediments in a way that we can measure directly."
The study, which was recently published in the journal Geology, explained that the 2013 storm dropped between seven and 18 inches of precipitation across Colorado's Front Range over a five-day period. Since this is equivalent to the average yearly rainfall for much of the region, more than 1,100 landslides of various sizes were triggered. This also caused flooding in every river and widespread property damage.
"We estimated the velocities of some of these debris flows at about 10 meters per second, which is as fast as sprinter Usain Bolt runs," Anderson said. "They're incredibly destructive because they happen so quickly and there's no warning system once a flow is triggered."
Since so much sediment is carried away in one mass wasting (settling and landsliding) event, and it takes a much longer process for the sediment to develop, Anderson adds that these events are not likely to happen often.
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