Not so much feet OF clay, rather feet IN clay

Now don’t get in a panic about this – we live here and it is interesting, not terrifying.

If you have ever had the inclination to think that history doesn’t affect you, especially the really old history, back before people trod our valley, then it is time for you to rethink that premise.

I had the occasion to speak with a young geotechnical engineer from McElhanney, Tyler Wilkes, who took the time to give me a brief lesson on the geological history of the Kitimat Valley and beyond; in particular, about marine clays, their chemistry and the implications of all this stuff for you and me.

Of course, being the curious type, Tyler’s lesson piqued my interest and got me started on a bit of an exploration that led me to a book by Marten Geertsema, David M. Cruden and John J.Clague titled Landscapes and Landforms of Western Canada, World Geomorphological Landscapes, Springer International Publishing, Switzerland, 2017. Wow, that was a mouthful.

In the chapter, The Landslide-Modified Glacimarine Landscape of the Terrace–Kitimat Area, BC, we learn that apart from a few hunks of rock sticking up here and there, and the odd parcel of sand or gravel, we the residents of Kitimat, Kitamaat and Terrace (and beyond) share the pleasure of sitting on top of a thick layer of marine clay left over from the last Pleistocene glaciation, somewhere around 12,000 years ago.

Along with Norway, Sweden and Ireland our fjords tend to have patches of a version of marine clays called “quick clay” or “sensitive clay”. This is weird stuff.

Now don’t get in a panic about this – we live here and it is interesting, not terrifying. Neither is this stuff everywhere, but it is here.

So, our tale. Marine clay was formed when the glaciers sat on our land and forced it down below sea level. The clay particles created from weathering, the grinding of the glaciers and other geological processes have teeny-tiny holes (voids) that were saturated with salt water.

That clay is fairly stable stuff – the different electrical charges between the salt water and minerals in the clay create pretty strong bonds. However, as the glaciers melted and the land rose as the weight lifted off it, the clay popped its little head above sea level and in time the fresh water that fell or ran on it washed out the salt water and replaced it with the stuff we drink – the game changed.

We now have areas of “quick clay”. Take a handful of moist quick clay and roll it into a cylinder and you have a clay cylinder, familiar to any kid who likes to play in the mud or big-kid potter who likes to do the same.

Put your clay cylinder into a bowl and add weight to that clay (not a lot of weight is necessary) and you’ll be witness to something quite bizarre.

The stuff suddenly turns into liquid and begins to flow like chocolate milk. Now, take your bowl of liquid clay, add some table salt, stir and back comes your familiar fun clay. It’s remarkable.

The liquefaction (the chocolate milk making thing) of marine clay is exactly what happened in the Lakelse slide of May 25, 1962.

That slide is familiar to most anyone who has been around the area for a time. It took out 1.1 km of new highway, transmission lines, and moved about 10 million cubic feet of land that travelled down a slope of about 1 degree or less. You probably wouldn’t notice such a slope if you were walking on it.

The slide seems to have been caused by loading of the road which was under construction at the time and the pressure sensitive quick clay turned into our metaphorical chocolate milk, spread and just kept going, more and more liquefaction occurring as it expanded and the whole mess flowing into Lakelse.

Really quite amazing. You might have thought that the hillside collapsed behind the slide, but you’d be wrong. In reality, the hillside stopped the collapse.

There apparently are numerous examples of such events throughout the valley: Nalbeelah Creek, the Onion Lake Delta, Hirsch Creek and Mink Creek to name a few. The latter was as large as the Lakelse slide and occurred in 1993-94.

YouTube even has an incredible video of one of these events that took place in Rissa, Norway, in 1978. Two photographers managed to get film of the Rissa slide as it happened. It is just incredible to watch.

Of course, from a natural perspective, these slides are not all bad. They help in valley formation, spawn biodiversity and are simply another part of the geological life of the planet.

It’s just at the interface between humans and the natural world that it is a problem.

You might ask, why put Kitimat and Terrace here then? Hmmm, well, where else would you put them? These conditions are apparently frequent in glaciated valleys that open onto the sea – pretty much where you’d like to put a port on our coast.

So, here we are, here’s the clay and we simply have to pay attention to how we live with the stuff.

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Terrace and Region Archives, courtesy Terrace Public Library.

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