They are always beautiful and often serene. But from earthquake potential to hailstorms, from lightning strikes to cliffs, fires, debris flows and avalanches, the Wasatch Mountains also can be dangerous.

On the lower end of the hazard scale is the danger to an individual, such as a rattlesnake bite suffered by a hiker in the mountain's foothills. On the upper end are the deaths, injuries and billions of dollars in damage expected if the Salt Lake County section of the Wasatch Fault were to slip violently, unleashing a 7.5-magnitude temblor.

Earthquakes

The Wasatch Fault runs along the western edge of the Wasatch Mountains, sticking out a bit on either end. It stretches from near the Idaho border to Fayette, Sanpete County, and is divided into several semi-independent segments. It is close enough to Utah's biggest population centers to cause major devastation during a big quake.

It's no coincidence that the Wasatch Fault runs beside the Wasatch Mountains. The geological forces that raised the mountains in the first place still lift them, and the tension between the mountains and the adjacent land causes the fault.

Envision the fault as a fracture plane that tilts toward the valley, said Walter J. Arabasz, director of the University of Utah Seismograph Stations. On either side, the landscape forms gigantic "blocks" of ground.

"The valley block has dropped downward and the mountain block has raised upward so that the Wasatch Mountains are basically the uplifted block bounding the down-dropped valley block along the Wasatch Fault," he said.

The fault is an angled plane between the two, reaching deep into the earth.

"The forces that are acting are trying to raise the mountains and drop the valley block, and there is a frictional contact between the Wasatch Fault," he added. "That friction keeps the blocks from slipping until the stresses become too great and the friction is overcome."

When the cohesive friction breaks, part of the fault "becomes unstuck and suddenly slips," he said. That slippage is an earthquake.

A glance at earthquake frequency along the Wasatch Fault can be chilling. In the past 5,600 years, researchers say, the Salt Lake segment of the Wasatch Fault unleashed powerful earthquakes about every 1,400 years. "The last one was almost that long ago," the Utah Seismic Safety Commission reported two years ago.

In other words, a monster quake could strike the Salt Lake Valley any time. But earthquake predictions are iffy, and a quake could happen tomorrow or in 100 years.