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Q&A — What you need to know about landslides

Published August 5, 2014 10:09 am

This is an archived article that was published on sltrib.com in 2014, and information in the article may be outdated. It is provided only for personal research purposes and may not be reprinted.

Did you know?

A slope does not have to be steep to slide. Slopes as gradual as 15 percent have slid when weak, clay soil is present.

Steep slopes with bedrock do not typically slide, but falling rock may be a danger.

Slides can occur even in dry years.

Most landslides occur in April and May.

Thousands of landslides — active and inactive — exist along the Wasatch Front.

State geologists say landslides are not inherently unstable but "moderately stable at best."

Which areas are prone to slides?

If it slid once, even in ancient times, it may slide again.

Steep, natural slopes with weak, clay soils or steep man-made cut-and-fill slopes.

Areas in or at the mouths of drainages, including bluffs overlooking streams.

Slopes below leaking canals or ponds.

Areas below cliffs or hills with outcrops of fractured rock.

What can cause a landslide?

Heavy rainfall, rapid snowmelt, excessive lawn watering, water or sewer-line leaks, canal breaks. If prior years were wet, slides are more likely.

Grading that removes earth from the base or loads dirt at the top or otherwise alters the slope.

Earthquakes.

You might be on a landslide if ...

Door frames are no longer plumb; windows start sticking.

Walls crack, indicating walls and frame are not aligned.

House makes intermittent creaking, snapping or popping noises.

Decks and patios tilt or move relative to the house.

Portion of road sinks or buckles.

Sidewalks crack, or ground, pavement or walks show unusual bulges.

Bare spots appear on slopes.

Dry areas start to show springs, seeps or saturated ground.

Foundation pulls away from soil.

Fence lines are askew.

Telephone poles, trees,retaining walls or fences begin tilting.

Water lines and other underground utilities break.

Common types of landslides

Debris flow: Sediment and water that flow down a hillside or streambed.

Rock fall: Earth and rocks that separate or fall from a cliff or cut slope.

Slide: A downhill movement of soil or rock often caused by saturated ground.

Tips for house hunters

If you're shopping for a lot or a home on or at the base of a hill or mountain, be sure to:

Do some double-checking. Don't assume it's safe just because the city or county approved it.

Go to the Utah Geological Survey website, http://www.geology.utah.gov, for information.

Go to the city or county planning office and ask to see geologic-hazard maps as well as all geologic and geotechnical reports for the subdivision. Ask to see the developer's and any independent reports.

Seek proof that expert recommendations were followed.

Possibly hire an engineering geologist or geotechnical engineer to evaluate the site or reports.

Source: Utah Geological Survey