Landslides

. (Photo by Ted S. Warren / The Associated Press)

                    This week, a significant landslide has been in the news. Whidbey Island sits in Puget Sound, about fifty miles North of Seattle, Washington.  It's an absolutely idyllic place where the families who live there make use of the recreational opportunities for their families.  Normally the families whose homes overlook Puget Sound are very lucky indeed, but not this week.  Landslides do occur in the area.  On March 27th, a terrible noise which locals said sounded like an explosion left one house down the hill, and  seventeen others isolated from the road, electricity and other services.  One man was removed from his home via ATV.  It's actually very lucky that no lives were lost. Later, additional homes were evacuated.  A section of a roadway, "Driftwood Rd." has been completely lost.  Engineers have not yet decided whether it will be safe for the evacuated families to return to homes to get their possessions.  They also do not yet know if other homes are at risk for landslide.
                    This section of Washington State and Whidbey Island in particular were shaped and created by the Vashon Glacier which advanced and then retreated 18,000 years ago, according to geologists. The remaining glacial till has unusual geology. Some of it may look like concrete and other portions silt, sand, and then clay.  As beautiful as it is most of the time, there are occasional collapses.


           Just like earthquake, landslide is not a standard feature in a Homeowners Insurance Policy.  Clients who want this type of coverage need to speak to their agents and specifically have such a rider added to their policy.  This is possible in some locations and not in others at the discretion of each homeowner's insurer in the US and Canada.

(Photo: Mike Siegel, Seattle Times)

This is the view from above the landslide. (Photo: Ted  S. Warren, The Associated Press)

The area from 2006 ( Photo:Ted S. Warren, The Associated Press)

 

After the landslide on March 27, 2013 (Photo: Ted S. Warren, The Associated Press)

Many areas other that Whidbey Island are prone to landslides:

  Some of the general signs of potential landslides are:    From USGS

• New Springs,, or  wet swampy areas that  have not typically been wet before.
• New cracks or unusual bulges in the ground, street pavements or sidewalks.
• Soil moving away from foundations.
• Ancillary structures such as decks and patios tilting and/or moving relative to the main house.
• Tilting or cracking of concrete floors and foundations.
• Broken water lines and other underground utilities.
• Leaning telephone poles, trees, retaining walls or fences.
• Offset fence lines.
• Sunken or down-dropped road beds.
• Rapid increase in creek water levels, possibly accompanied by increased turbidity (soil content).
• Sudden decrease in creek water levels though rain is still falling or just recently stopped.
• Sticking doors and windows, and visible open spaces indicating jambs and frames out of plumb.
• A faint rumbling sound that increases in volume is noticeable as the landslide nears.
• Unusual sounds, such as trees cracking or boulders knocking together, might indicate moving debris.

Areas for which you should have landslide concerns:

• On existing old landslides.
• On or at the base of slopes.
• In or at the base of minor drainage hollows.
• At the base or top of an old fill slope.
• At the base or top of a steep cut slope.
• Developed hillsides where leach field septic systems are used.     (Don't park your car or truck on your septic field, even when delivering mulch)

Usually safe from landslides:
       

• On hard, non-jointed bedrock that has not moved in the past.
• On relatively flat-lying areas away from sudden changes in slope angle.
• At the top or along the nose of ridges, set back from the tops of slopes.

 
Remember always to have a "Go-bag" or Family Evacuation Kit packed and ready to go.



More information about landslides in general comes from the US Geological Survey:

http://landslides.usgs.gov/



Some of this information was obtained by:

More information from:

http://seattletimes.com/html/localnews/2020655560_whidbeylandslidexmlxml.html?prmid=obindomain

http://landslides.usgs.gov/