Clastic Dikes and the Sendai Earthquake

Written by E. Philip Small on March 19, 2011

The Landslide Blog posted on a fascinating video of muddy water pushed out of soil fissures during the Sendai earthquake. What you are seeing in the video (1:30, 2:35) may be how our Inland NW clastic dikes were formed.

In the Inland Northwest USA we have extensive slackwater sediments left by multiple glacial flood events. Most are in Washington State (see map of Lake Lewis). In some places, they are shot full of clastic dikes, a concern because they might provide a preferential pathway for contaminants reaching groundwater.

Short circuiting of contaminants down dike structures is enough of a concern that Washington Department of Ecology has us assess clastic dike presence during siting studies of industrial wastewater sprayfields (see WDOE-9336, page 12).

An actual occurrence of this type of pollutant short circuiting is yet to be documented, but that doesn’t keep clastic dikes from being one of the more fascinating features of Washington soils and geology.