2013’s Historic Storm Caused 1000 Years Of Erosion In Boulder Canyon
The 2013 storms in Colorado flooded streams across the region, washing gravel and soil into many rivers.
The storms also caused landslides and removed a thousand years’ worth of eroded rock and soil from some of the hillsides in Boulder Canyon, according to a study from researchers at the University of Colorado in Boulder.
“That’s what was so exciting in this storm,” says Suzanne Anderson, a geography professor at CU-Boulder and one author of the study. “There were some spots where the amount of material that was lost was substantial, and we could measure it.”
Erosion is actually quite hard to measure. Sometimes researchers can estimate erosion rates based on how much sediment floats down a stream or river, but that’s only one moment in a thousand years of data, and one aspect of a complex process that forms soils.
If we understand soil production there, it helps us understand soil production in other places of the landscape where we do grow trees or grass or crops.
Many times researchers don’t have enough photographs to compare how an area changed many years ago. If they do have photos, the changes that occur from year to year are so small that it’s often hard to separate soil changes from changes in tree cover or rocks in any given region.
The storm that brought historic flooding up and down the Front Range changed that. There was a direct before and after effect.
The researchers found that on average, the hillsides in Boulder Canyon lost material that it would have taken four hundred years to form through slow geologic events like weathering and erosion. Some areas lost as much as a thousand years’ worth of eroded rock and sediment.
All the eroded material washed down from the canyon, either steadily with the rain or through more sudden events, like landslides.
“We want to be able to identify these are places that are prone to producing landslides,” says Anderson. Understanding how sediment moves over the landscape may help predict which areas are at risk of landslide in future storms.
Anderson and her collaborators used soil chemistry to help determine the erosion rates around Boulder Canyon. When the beryllium in rocks is exposed to air, it comes in contact with oxygen, and it forms a different type of beryllium. Anderson could look at the levels of oxygen-touched beryllium, and determine how quickly the rock gets exposed to the air, telling her how quickly the rock eroded.
In addition, every piece of sediment displaced by the storms made its way downstream, piling up in rivers or adding to soils in Colorado. Even though Anderson didn’t specifically look at these accumulations, everything she learned in this study can aid people’s understanding of how soils form.
“Not that we’re growing things on the canyon walls in Boulder Canyon, but if we understand soil production there, it helps us understand soil production in other places of the landscape where we do grow trees or grass or crops,” says Anderson. “It’s part of understanding soils.”