Friday, March 30, 2012

Quick Clays and a Disaster Movie

Some of the worst landslides in history are the result of quick clays. I have been doing some research on why we do not, at least as far as I know, have quick clays in Washington State. Quick clays are associated with areas that were glaciated with thick heavy masses of ice during the last glacial period: Norway, Sweden, parts of eastern Canada and Alaska. The idea is that the huge mass of glacial ice in these areas during the ice age pressed the local land surface downward. As the ice melted these depressed areas were flooded by sea water. Clays were deposited on the sea floor of these areas before the surface area was able to rebound from the mass of ice. Under the right circumstances the clays that were deposited are subject to liquefaction with enormous landslides even on very gentle slopes. Hundreds of people have been killed in Norway and Sweden and dozens in Canada by quick clay slides. In Canada, an entire town was vacated and moved due to the risk and within two years the area completely failed.

What got me thinking about quick clays was this page vitenskap-og-teknologi with a video of a couple of geologists or geotechnical engineers doing some field work on a quick clay investigation. I liked the video as it shows what geotechnical drilling work can be like. The clip shows how quick clays can be readily identified with a simple on site test. Its is a very short video and might be difficult to understand unless your fluent in Norwegian, but will give one a sense of one aspect of geotechnical work.

There is a remarkable video that circles about amongst geo types and includes a bit of a description of how quick clay forms, where it is found, and a lab demonstration; however, the remarkable part is it has footage of a very large quick clay landslide. The video is a bit "old school", but worth watching if your into disaster movies. I really liked the way the remaining hazard areas were stabilized after the slide.

In regards to the lack of quick clay problems in Washington, I want to do a bit more reading on the subject and think through how the glacial marine clays underlying a fair bit of northwest Washington are different.


entropy said...

That's truly a fascinating film. I miss some of the methods of old-style science reporting, so thanks for sharing.

Sam Crawford said...

Wow, talk about Matthew 7:24-28! Great movie Dan.

Dan McShane said...

Thanks. I had to look up Mathew; that Jesus was a geotech is often overlooked. Good advice about finding builing sites.

wynneforplants said...

er... I wonder if this might apply to the deep marine clay-gravel layer over bedrock on the hill above Legoe Bay on Lummi Island? Gives a whole new meaning to why digging small holes -- like house foundations-- need to be done at the right time of year.