New maps point out geological hazards near Zion National Park

Published: Monday, March 17 2014 12:17 p.m. MDT

Virgin river in Zion National Park. To help administrative and planning officials, as well as consultants and homeowners, the state released a new set of maps that identifies the kinds of geologic hazards that may impact existing and future developments near Zion National Park.

Matt Gade, Deseret News

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LA VERKIN, Washington County — The communities of La Verkin, Virgin, Rockville and Springdale are subject to a variety of geological hazards.

To help municipal, county, regional administrative and planning officials, as well as consultants and homeowners, the state released a new set of maps that identifies the kinds of geologic hazards that may impact existing and future developments near Zion National Park.

The maps spotlight areas with 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 Knudsen, 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 state Route 9 study area covers 97 square miles and consists of a corridor ranging from about 2 to 8 miles wide and 15 miles long centered on the route.

The new publication fills in gaps between previous geological studies done for the St. George area. It includes nine different hazard maps that Knudsen 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," Knudsen said.

Every community has its own problems.

"Springdale has had a history of landslides, particularly in 1992," Knudsen 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."

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

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,” Knudsen 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, Knudsen 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.

Email: dcawley@deseretnews.com

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