Why the Oso Landslide Caused So Much Death and Destruction

The March 22, 2014 Oso Landslide in Washington was the most deadly landslide on record in the United States. Forty three people were fatally injured in a matter of seconds. The slide devastation covered more than 200 acres. The distance from the top of the head scarp to the furthest limits of the landslide impact was over 6,000 ft. The elevation difference was about 600 ft. More than 20 homes were destroyed in a matter of seconds. Before and after images taken by the author will be used to show how he thinks this slide occurred and why the destruction was so severe. In 2002 the author first photographed and examined the site. Since then, the author has made more than 60 flights over the site at various times and taken more than 1,000 images over the 12 year period. The slide area has been periodically moving for more than 100 years and has been examined by others prior to the author’s involvement in 2002. The most recent previous slide at this site occurred on January 25, 2006. It was different from many of the previous slides, and possibly larger than any those that have occurred at the site in the last 80 years. Images taken before and after the 2006 landslide demonstrate the differences in the mechanisms of the 2014 slide and all documented previous slides. The photographs give strong clues about why the 2014 slide was so destructive. Others studying the landslide have unofficially implied it was a deep seated landslide and then later a debris avalanche flow. The author is convinced it was neither. The author will use his pictures and long term observations to show what he believes happened at Oso.