Monday, June 18, 2007

The Dock Filter

Fishing on the dock this weekend reminded me that it is a perfect bastion against negative geology thoughts. There, I believe that if you can't say anything nice about certain geology, then don't say anything at all! This was the Weekend of the Dragonfly, since they were especially dense, and constantly climbing out on the dock, doing their amazing changing act. Swooping all around us, they were our Terabithian Warriors, chasing bad thoughts and mosquitoes!

I can talk about the bad geology of the Ottawa region, since it is on the very fringes of Ontario. A long time ago, we were actually looking at putting in a nuclear plant at Chat's Falls, just north of Ottawa. A quick workup of the geology and seismic hazard, put the seismic design basis at a level beyond our ability to design, and the project was quietly dropped.

Ottawa used to be as good as the best rock in Ontario, but got hammered by the Wilson Cycles, which are the repeated opening and closing of the oceans that have been going on for the last few billion years. The opening before the current Atlantic opening was the formation of the Iapetus Ocean. When this happened poor Ottawa got ripped apart with the Ottawa-Bonnechere Graben which is an aulocogen (failed rift). You can really see the rip in the DEM images!

That wasn't enough for Ottawa! When the current Atlantic started opening, the Great Meteor Hotspot was passed over, leaving a giant track of volcanism and fractured rock. Think of a giant key being dragged over the underside of the continental car body!

Here's a graphic of some of the mess around there.

I've managed another one of my fancy DEM's for a section of the Ottawa Graben.

You can see the straight gashes on both sides. As if that weren't enough, Ottawa then got dunked into the sea by the glaciers, and all sorts of marine clay was deposited. As mentioned in this article (started by me) quick clay is nasty stuff. It can turn into soup, right under your feet.

So, three cheers for Ottawa, which acts like it isn't part of Ontario anyway..


monado said...

Of course that got me wondering what a graben was, since it's a long time since my Grade 10 geology class. Does this mean that one day the ocean will open up again under Ottawa's collective feet?

Courtney said...

Hey there! I know it's been a while, but where did you find that image you describe as "Here's a graphic of some of the mess around there"? I would love to cite it (and you!) on my blog.