New maps point out geological hazards near Zion National Park

New maps point out geological hazards near Zion National Park

(Utah Dept. of Natural Resources, Geology.utah.gov)


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SALT LAKE CITY — The state has released a new set of maps designed to tip off developers and homeowners to potential geological hazards in communities near Zion National Park.

The maps address hazards such as potential for flooding, falling rocks, unstable soil and erosion. Some geologic hazards are obvious, but others — like collapsible or swelling soils — are much more subtle, according to Tyler Knudson, project geologist with the Utah Geological Survey.

“The purpose of the maps is basically … to help guide future development and also to help existing development with hazards that could pose a threat,” he said.

The new publication fills in gaps between previous geological studies done for the St. George area. It includes nine different hazard maps that Knudson said can be a tool for planners as they guide growth.

“It’s kind of a red flag for what kinds of hazards and adverse construction conditions they can expect as they go into these areas,” Knudson said.

Every community has its own problems, he said.

“Springdale has had a history of landslides, particularly in 1992,” Knudson said. “There was a magnitude-5.8 earthquake 30 miles away in St. George. Even though it was 30 miles away, it ultimately took out an entire subdivision there in Springdale,” Knudson recalled.

Springdale also has experienced a couple of other landslides since then, he said.


Springdale has had a history of landslides, particularly in 1992. There was a magnitude-5.8 earthquake 30 miles away in St. George. Even though it was 30 miles away, it ultimately took out an entire subdivision there in Springdale.

–Tyler Knudson, geologist


Communities like Springdale, Virgin and La Verkin are projected to continue to grow, while growth in Rockville is considered “stagnant.” In that case, the new report may help prospective homebuyers and builders replacing existing buildings with new ones.

The report also notes that the Virgin River, close to all the communities mentioned above, flooded in 2005 and 2010.

“I think people are becoming more aware, and the standard of practice for identifying these areas is better,” Knudson said.

The report offers recommendations for residents of hazard areas. For example, homeowners in a potential rock-fall area could try to make room to deflect rocks, if they have the space. Or they may decide to move and retire the property, Knudson said. The least desirable option may be to continue to live there and accept the potential consequences.

A boulder crushed a home in Rockville, killing two people, in 2013.

Developers building on problem soil would have several options, including bringing in non-native soil.

Similar maps are being developed for the Salt Lake and Utah County areas, as well as Cedar City. They should be available in the next year or two, Knudsen said.

Geologists compiled the new information using existing geologic maps. Those for Cedar City were 40 years old, so the area had to be remapped, Knudsen said. Geologists used specialized computer software and gathered geological data such as soil tests from developers to build the hazard maps.

Contributing: Linda Williams

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