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Environment

This Map Shows Parts Of Boulder County Susceptible To Landslides

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Jonathan Godt
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U.S. Geological Survey
The 2013 rains catalyzed hundreds of landslides; this large one, which wiped away buildings, took place on the northwest side of Twin Sisters Peak outside Rocky Mountain National Park.

The devastating 2013 floods have left their mark on Colorado's landscape, and that includes an increased risk of landslides in areas that received heavy rains.

"In some of the areas, the soil became unstable. It moved, but it didn't totally fail and flow down the slope. So it's at a reduced strength, and those areas are unstable," said Karen Berry, who directs the Colorado Geological Survey and is the interim state geologist.

There were hundreds of landslides during the floods, Berry said, and the lack of stability now means some areas will continue to slide. That's why the Survey is making maps showing the areas of Boulder and Larimer County at increased risk for slides.

They've completed a debris flow risk map for Boulder County, and are almost done with the one for Larimer too.

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Credit Colorado Geological Survey
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Colorado Geological Survey
This map, from the Colorado Geological Survey, shows Boulder County areas at risk for debris and mud flows.

There is also increased risk for rock falls, said Berry – so the Survey is mapping the risk of that too, and will give those maps to Boulder and Larimer Counties.

"In some areas you've got large boulders that have moved down the channel, and in some areas they are kind of precariously perched," she said – above homes or roads, and with additional rain, the rocks could fall again.

Berry said the counties can use their new maps to prepare for emergency scenarios. They can also be used for planning future development and ensuring it is out of the way of potentially dangerous areas.

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