Big Sky, Past and Future
Scientists See Landslide Risk in Big Sky
The weak shale formations of Big Sky create ripe conditions for landslides. For property buyers, it's caveat emptor. This story is part of a series about Big Sky produced by University of Montana School of Journalism students in collaboration with NewWest.Net. Video by Kip Sikora. Story by Elizabeth Diehl and Megan McLean.By Kip Sikora, Guest Writer, 8-28-09
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It’s the spectacular mountains that make Big Sky, Montana what it is, but geologists worry that they’re less solid than they seem. The shale formations in many parts of Big Sky are susceptible to landslides, and many houses have been built in areas that could start moving if there’s a period of exceptionally wet weather.
And because Big Sky lies within the Intermountain Seismic Belt—the part of the intermountain west with the highest earthquake potential—risk of sudden landslides is that much greater.
In 1959, an earthquake with a 7.5 magnitude struck part of Madison Valley, about 30 miles south of the Big Sky-Moonlight Basin area, triggering a landslide that killed 28 people. After damming a section of the Madison River, this event coined the name “Quake Lake.”
How developers, brokers and home buyers in Big Sky deal with the landslide risk is all over the map. In many cases buyers are aware of the problem and invest in engineering solutions, but in other cases they’re in the dark. As reported on NewWest.Net, a recently settled lawsuit against the Spanish Peaks development alleged that known risks were not disclosed, and that the sales staff was told to “baffle them with BS” if people asked about the issue.
Geological surveys and soil-sampling are generally required as part of the subdivision approval process, but those reports are not always shared with buyers. In the accompanying video story, several experienced geologists discuss their concerns.
The map below, from Susan Vuke of the Montana Bureau of Mines and Geology, shows known landslides in Big Sky. Click the image for a larger version or click here for the a PDF.
This story is part of the Big Sky, Past and Future series. Click on the headlines below for previous stories and check back for new installments at NewWest.Net/BigSky
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Comments
In 1925 a 7+ quake struck near Manhattan, MT, and just 50 years ago the 7+ Hebgen Lake quake, just 30 miles south of Big Sky, killed 29 people...........I guess sitting on top of the Yellowstone Super Volcano and nearby earthquakes are nothing to fret over.
Big Sky has a very high risk of a large quake. 88% prob of a 5.0 or greater in the next 50 years.