What Were You Feeling at 5:30 Yesterday Morning?

Snow College Seismograph 

5:30 a.m. 

Recorded It. 

UTAH HISTORY TO GO 

Geologic Hazards

It should come as no surprise that the geologic processes that blessed Utah with an abundance of material resources and a variety of natural features distributed an equally diverse suite of geologic hazards across the state. The geologic processes that shaped the landscape of Utah present significant hazards to people and property. Utahns are exposed to earthquakes, landslides, mud flows, rock falls, avalanches, flooding of rivers and lakes, radon, and problem soils that shrink, swell, or compact. These hazards can be costly, and some threaten lives. For instance, during the five-year period from 1982 to 1987 landslides, rising lake levels, debris flows, high groundwater levels, and floods caused hundreds of millions of dollars in property damage along the Wasatch Front and in central Utah and killed three individuals.

Some hazards are rare events with high risk such as earthquakes. Others are generally not life-threatening but are more frequent and cause considerable damage, particularly when they are ignored or exacerbated by construction practices. Earthquakes are the most destructive, but not the most frequent, geologic hazard in Utah. Large earthquakes have occurred and will continue to occur in the western two-thirds of the state, and geologic evidence and the historic seismicity indicate that such events are more frequent in a zone trending along the Wasatch line. Displacements along a zone of faults account for the location of the Great Salt Lake and Utah Lake on the down-dropped side and impressive mountain fronts on the upside. Present scientific understanding of the faults does not provide a basis for predicting when and where the next earthquake will occur. Estimates of the maximum magnitude of a Wasatch Fault earthquake range from 7.0 to 7.5 on the Richter scale. This type of earthquake will affect some area of the Wasatch Fault on the average of once every 300-400 years. Ground-shaking over a broad area is the single greatest hazard associated with earthquakes because shaking causes buildings to collapse, and the falling materials kill people and destroy property. Surface rupture, the shifting of location of lakes, failure of dams, landslides, lateral spreads, mudflows, liquefaction, piping, other hydrologic changes, and waves on enclosed bodies of water also can and will cause extensive damage depending on the location and magnitude of an earthquake.

Landslides and flooding are the two most common geologic hazards in Utah and annually cause significant economic losses. Approximately 45 percent of the state is mountain, hill, and steep-valley terrain conducive to landslides. Also, some geologic formations in Utah are particularly prone to develop landslides. Summer cloudbursts and rapid snowmelt have flooded many Utah communities. Fortunately, the conditions that produce landslides and flooding are quite well understood, and intelligent use of geologic information in land-use planning can minimize the negative impact of landslides and flooding.

Conclusion

The geology of Utah has contributed much to the economic development of the state and offers many recreational opportunities to residents and visitors. It is a major factor in making Utah an attractive place to live and visit. The geology must be respected, however, or it can cause great property damage and loss of life. Also, much of the geology is fragile and must be protected from abuse if it is to be available to future generations. Wise development of the state requires a knowledge and a respect for its geology.

See: William Lee Stokes, Geology of Utah (1986).