NOVA PBS on landslides and Oso — (Airs November 19, 2014 at 9 pm on PBS)
Liesl Clark of Bainbridge Island is the writer, producer and director of “Killer Landslides.” Here’s what she had to say about the slide and the documentary:
“The film provides viewers with an overview of some of the causes of landslides like the one that happened in Oso/Darrington. We also point to telltale signs as seen on other slopes around the world, like slumps in a slope’s topography, cracks at the crown of a hill, and smaller slides that form on slopes that are beginning to fail. The film looks at the specific geologic materials on Hazel Hill, the slope above the community of Oso that slid, and shows the value of LiDAR imagery on sloping terrain that is of concern. LiDAR can provide visual information about past landslides that might have occurred in any area, indicating a pattern.
I looked up the LiDAR imagery for my neighborhood, for example, on the south end of Bainbridge Island and was surprised to see that my house is situated at the head scarp of an ancient landslide that occurred here, the only one on the island. It doesn’t help, that we’re also next to the Seattle Fault line. This is all visible through LiDAR. Now I’m going to be particularly interested in studying the nearby topography for signs of slippage, will watch for increases in precipitation, and might even get a geologist’s report on the geologic materials that our home is sitting on and share that with neighbors.
The more informed we are, the better we can make decisions as homeowners and keep an eye on the slopes around us.”
University of Washington geologist David Montgomery, an expert for the documentary of the Oso event and author of “The Rocks Don’t Lie: A geologist investigates Noah’s flood.” had this to say.
“The Oso landslide reminds us of the need to understand the nature of the, at times violent, processes that shape Earth’s dynamic surface. Some landslides can run out very long distances, and the way that a particular landslide has behaved in the past may not necessarily forecast how it will behave in the future. While LiDAR data can provide us a much improved view of where past landslides have occurred, and to predict hazardous areas, we still need geological field work to determine the ages of past landslides to get a handle on often they occur (and recur) and how many of the largest ones are triggered by earthquakes versus period of high precipitation.
But in general, our wet climate in combination with steep valley walls and coastal bluffs made of relatively weak, glacial age geological materials makes western Washington landslide country.
And yet landslide hazards and risks are probably the least studied and constrained of the natural hazards that influence the region, in part because earthquakes and volcanic eruptions capture the imagination of geologists and the public alike.
There remains a lot of work to do to in mapping landslide hazard zones, including their potential runout zones, understanding risks, and communicating that information to the general public in ways that can be readily understood by non-geologists.
This tragedy is also a sobering reminder that when a really big landslide mobilizes the only safe place to be is out of its way.”