WC can report a new and entertaining way to
waste time assiduously study on the internet. Sometime in 2016, the United States Geological Survey created an on-line, interactive geological map of Alaska. If you are a geologist, professional or amateur, it’s about as cool a toy as the Series of Tubes™ has to offer. WC is hardly the most qualified person to show all the spiffy features, but if absence of qualification were a barrier to this blog, the blog wouldn’t be here.
Here’s a screen capture of the area around Yakutat, in southeastern Alaska. It’s one of WC’s favorite spots in Alaska.1
The different colors identify different kinds of surface rocks or features. Maps of this kind mostly just show surface features, not what’s under the surface. That’s an inference.
The gray lines are faults.You can see Yakutat Bay in the middle, running north to Disenchantment Bay and Hubbard Glacier where it makes a 120 degree turn in to Russell Fjord, with the fault trace of the massive St. Elias Fault running along its length. You can zoom in an out, and see the identification of the rocks. Clicking on a spot brings up a window showing the kind of rock at that location.
The bright pink, for example, has the symbol Toegr, which tells you it is an relatively young igneous rock (Tertiary, early Oligocene and Eocene, 56 to 28.1 million years ago). You can click on the symbol name for more information about that particular kind of rock.
Yakutat sits on a sub-block of the Chugach Terrane, and was likely the last piece to arrive at North America.2 Almost immediately after colliding, it began sliding northwesterly along the St. Elias Fault. You can see the dislocation in the pieces of Toegr on either side of the St. Elias Fault. That’s what WC means by inferences you can draw from a map like this.
You have control over what information appears, and you can control the opaqueness of each layer.
There’s probably much more, but WC is still exploring.
And, if you will excuse WC now, he’s going to get back to exploring.
- And not just because the best steelhead fishing in North America is on a nearby river. Seriously, any place where there are 18,000 foot tall mountains less than 20 miles from tidewater has to get a geologist talking to themselves. ↩
- To paraphrase John McPhee, most of Alaska, like most Alaskans, originally came from somewhere else. Alaska seems to be composed of as many as 50 terranes and blocks of terranes that collided with and stuck to the North American Craton, the core of the North American continent. ↩