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July 2013

On July 18, DGER Chief Hazards Geologist, Tim Walsh, led a field trip for FEMA officials and their international counterparts from Australia and New Zealand. While traversing Elliott Bay on the Seattle-Bainbridge Island ferry, he spoke on the subject of earthquake and tsunami threats to the Seattle area, recounting evidence of Seattle Fault activity and associated tsunami events located along the route. The Australian and Kiwi emergency managers reflected on their own personal experiences during the ensuing discussion on the impacts and mitigation of geological disasters, as similar dangers exist along the coasts of their home countries. The field trip took full advantage of a gorgeous summer day on Puget Sound (the kind that leaves visitors wondering if Washingtonians don't greatly exaggerate about their relentlessly rainy weather), and the participants were very appreciative of the region's great beauty. This popular field trip, which Tim has led on a number of occasions, was specially requested by FEMA organizers, and DGER was happy to help out!
Seattle-Bainbridge field trip
Tim Walsh discusses Seattle-area geologic hazards with FEMA officials and emergency managers from Australia and New Zealand during a Seattle-Bainbridge Island ferry ride. Image courtesy of Meredith C. Payne, DNR.

Ghost Forest near Copalis Beach
July Geology Image of the Month

July's geology image of the month was taken by Mapping Geologist Michael Polenz. The pictured ghostly tree trunks of once-submerged red cedars have played a key role in helping geologists reconstruct the events of the last Cascadia Subduction Zone (CSZ) magnitude 9 earthquake. As DGER chief hazards geologist, Tim Walsh, recently explained to a National Geographic television crew (see image below), the combined use of radiocarbon dating and tree ring analysis on these tree trunks allowed dendrochronologist David Yamaguchi (University of Washington) and geologist Brian Atwater (U.S. Geological Survey) to date an episode of sudden coastal subsidence that drowned the trees in seawater and killed them approximately 300 years ago (sometime between August 1699 and May 1700). This time frame also coincides with numerous accounts of a tsunami of unknown origin that reached Japanese shores on January 26, 1700.

In The Orphan Tsunami of 1700 Atwater, Yamaguchi and their coauthors were able to correlate that tsunami with a CSZ megathrust earthquake that triggered the land subsidence and inundation event that submerged coastal forests in the Pacific Northwest. In relating the orphan tsunami to the subsidence event at the Copalis River pictured here, Kenji Satake (Geological Survey of Japan), Kelin Wang (Geological Survey of Canada), and Atwater reviewed the size, character and timing of tsunami waves along the Japanese coast and inferred that the wave train matched what would have been expected from a magnitude 9 Cascadia Subduction Zone earthquake.


The earthquake of 1700 is the type of Cascadia megathrust earthquake we expect to reoccur in the Pacific Northwest at any time. It rivaled the magnitude and character of the Tohoku earthquake that devastated northern Japan on March 11, 2011. To Michael Polenz, the geologist who took these photographs, "it all adds up to a remarkable piece of geologic detective work, wherein coastal stratigraphic geology field work was combined with dendrochronology, ocean wave modeling, and historical research of municipal records on another continent to reveal the story of massive earthquakes here in Washington."   


We welcome public contributions for the Geology Image of the Month feature. The images have pride-of-place as our header image for our blog site, www.washingtonstategeology.wordpress.com, for the month, and are archived in the blog site's Image Gallery.

If you have a Washington geology image that (1) you have the rights to share, (2) can be cropped horizontally to fit our header space, and (3) for which you have a detailed description of the subject matter, contact us! We'd love to show off your great pics! 

Sultan quadrangle pseudo-3D image
3D PDF of the Sultan quadrangle available for download from the Subsurface Geology webpage.
What's New on the Web?
The gradual evolution of our webpages at www.dnr.wa.gov/geology continues! Already you can find the new pages for:

The Subsurface Geology page hosts the downloadable 3D PDF files that allow the user to view relationships between topography, surface geology, and subsurface geology (represented by cross sections and borehole data). Files can be viewed and manipulated with Adobe® Reader®. Sultan is currently available for download, and other quadrangles will be coming soon!  

What's New on the Portal?


The geologic information portal is still in the process of being migrated to the latest version of ArcServer (10.1). The release will herald an updated version of the Geothermal Resources theme and a new Natural Hazards theme. Stay tuned!
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At Left: Chief Hazards Geologist, Tim Walsh, explains how this ghost forest near Copalis Beach provides evidence that the CSZ is capable of producing an earthquake of magnitude 9+.

The film produced by National Geographic highlighting the Copalis ghost forest is called "Countdown to Catastrophe: Mega Quake" and can be found on YouTube.
Washington State Department of Natural Resources | 360-902-1000 | bob.redling@dnr.wa.gov | http://www.dnr.wa.gov
1111 Washington St. SE
Olympia, WA 98501

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