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News Release May 7, 2002
GSA Release No. 02-29
Contact: Ann Cairns
Director – Communications and Marketing, 303-357-1056

Geologists to Discuss Landslide Hazards

Every year in the United States, landslides cause two billion dollars in damage and about 25 to 50 deaths. While landslides occur in each of the fifty states, the most problematic areas are the Pacific Coast, the Appalachian Mountains, and the Rocky Mountains.

Closer to home, Mother Nature has been wrecking havoc in Utah with the Layton landslide last August that destroyed three homes and may still be a continuing threat. What's even more perplexing is that no one is sure what caused it.

Landslide hazard experts from South Dakota, Colorado, and Utah will come together May 8 at a special session of the Geological Society of America Rocky Mountain Section Meeting to share their expertise and insight into this complicated natural threat. The session on Hillslope and Mountain Slope Hazards in the Rocky Mountains will take place on the Southern Utah University campus.

One goal for this session is to share information about these hazards with citizens and community leaders. Peter D. Rowley, from Geologic Mapping, Inc. in New Harmony, Utah, will discuss Zion National Park's rockfall and landslide hazards that have plagued nearby Rockville and Springdale.

"The rock that destroyed the home in Rockville is huge, and still sits in the middle of the house as the homeowner tries to deal with his insurance company. That image remains so horrendous that it alone made me want to give this talk," Rowley said.

What Rowley has found is that the deep narrow canyons that bring tourists to the south entrance of Zion National Park also bring a share of natural landslide, rockfall, and debris-flow hazards to homeowners, public lands, and tourists in the Rockville and Springdale areas.

Debris flows are another danger that we need to better understand. Debris flows can strike without much warning and they can easily destroy structures in their path. That's why it's crucial to evaluate debris-flow hazards to keep people safe and prevent property damage.

Richard Giraud from the Utah Geological Survey will introduce new guidelines to help geologists evaluate debris-flow hazards on alluvial fans in Utah. The Utah Geological Survey will publish the guidelines.

"The guidelines outline geologic methods to evaluate debris-flow hazards and understand how often these flows of mud and rocks are deposited on alluvial fans and the potential impacts these flows can have on development," Giraud said. "The areas most prone to debris-flow hazards are alluvial fans that lie at the bottom of steep drainages." Alluvial fans are fan-shaped deposits of sand, gravel, and boulders that are favored sites for development.

David A. Scroggin, from Jack Johnson Company in Park City, Utah, will introduce a new avalanche hazard map for Salt Lake County. The new map will help decision-makers discern if an area would need specific avalanche hazard analyses before land use proposals could be considered. The map is a combination of known avalanche paths, delineations of new avalanche influence zone boundaries based on digital terrain analysis, stereoscopic aerial photographs, field observations, and historical research.

Recent studies revealed that development in some locations was approved before avalanche hazards were required to be considered in the zoning review process," Scroggin said. "There is continued encroachment into valuable mountain bench and hillside areas. So we needed to provide guidelines that would enable planners to identify when special studies should be required."

David B. Simon, from Simon Bymaster Inc. in Salt Lake City, will share his discovery that a proposed site for a reservoir was potentially landslide-prone. His presentation is a good example of why geologic studies of an area are crucial before projects are approved. Simon and his team investigated a site in Pleasant Grove in eastern Utah County using geologic mapping, aerial-photographs, and exploratory trenching. Initial investigation of the site using only engineering borings did not reveal the potential landslide hazard.

"What is most important is that the decision-makers listened and accepted the geologic recommendations and found a new, geologically stable site for the reservoir." Simon noted. "As urban growth encroaches into foothill areas of eastern Utah county, recognition of these relatively large landslide features and their implications for safe development become ever more critical."

Contact information:

Peter D. Rowley
Geologic Mapping, Inc.
P.O. Box 651
New Harmony, UT 84757
Richard E. Giraud
Utah Geological Survey
1594 West North Temple, Suite 3110
Salt Lake City, UT 84116
David A. Scroggin
Jack Johnson Co.
1777 Sun Peak Drive
Park City, UT 84098 USA
David B. Simon
Simon Bymaster Inc.
1981 East Curtis Drive
Salt Lake City, UT 84121

Geological Society of America
Rocky Mountain Section Meeting
May 7-9, 2002
Southern Utah University, Cedar City, Utah

For information and assistance during the meeting, please call the GSA registration desk at 435-865-8437.


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