I've been hiking this week around the Kootenay Lake region of B.C., Canada. It's spectacular country. So, we climb up through forest, and eventually come out into alpine meadows and valleys, some of them covered with a moonscape of enormous boulders left behind by the glaciers. The whole area was once under two miles of ice! Our guides always tell us that the boulders are left behind by the glaciers when they melt. Also, that the boulders are worn smooth and more or less round by being tumbled over and over by the moving ice. Sort of a geologically slow rock polisher. So, here is my question: Are the boulders picked up by the glaciers in the first place as individual chunks of rock, previously broken off by other geological processes, or are they broken off the solid rock of the mountain by the glacier itself? Now I have a day off from hiking. I drove up to Revelstoke this morning, and tomorrow morning I helicopter in to an isolated and rustic lodge for another week of hiking. I'll have no internet access or telephone from tomorrow morning until I get home. Here's hoping I don't fall off a mountain or get eaten by a grizzly bear.
I really thought this was a you tag thread - until I noticed I was lurking as guest =) It's really a combination of both - anything unlithified in the path of a glacier can be easily assimilated, but there's so much weight behind a glacier that they can break off pieces (even huge pieces) from the bedrock along natural fracture lines. Oh, by the way? I want to live your life for a little while =) Really, I can't think of anything that sounds better right now than helicoptering to an isolated lodge for a week of hiking. Beautiful country you have in your backyard - enjoy your trip.
Geologyrox covered it. Keep an eye out for cirques high up in the valleys where you are working and maybe you can see if the erratics are of the same rock type and that could help you understand their origin and if they have been ice wedged then plucked or if they have been transported from somewhere else. Cirque (Tioga Pass/Yosemite) Glacial Polish in granite/xenolith Xenoliths in granodiorite? I have a bunch of pics on a lil video I put together for our lil expedition group when we were in the White/Inyo Mountains and Eastern Sierra a couple weeks ago. Most of the pics are form 8,000ft to 14,246ft above sea level so might be similar types of terrain despite our lower latitude. http://fatalfoo.com/Movies/White%20Mountain%20Trip_0001.wmv
My mother, the geology teacher says: "Are the boulders picked up by the glaciers in the first place as individual chunks of rock, previously broken off by other geological processes, or are they broken off the solid rock of the mountain by the glacier itself? The answer is yes. Boulders are carried along in the glacier. They are usually from a rock formation that is different from the bedrock on which they rest. Also, the striations on the boulders show the direction of retreat of the glacier which scratched the rock as it went back. Actually, Wikipedia has the correct answer http://en.wikipedia.org/wiki/Glacial_erratic" And, says Rufaro, mother of a teenager, aren't mothers always right?
Oooh, some nice pictures. My vote for a really exciting new thread: Igneous Petrology! :lol: Go! Excuse me, I've got to go clean out my terminal moraine...
<div class='quotetop'>QUOTE(Rufaro @ Aug 31 2006, 03:57 PM) [snapback]312424[/snapback]</div> Clicking on this link, Wikipedia says it does not have an article on this subject. But thanks to geologyrox and others for your information.
<div class='quotetop'>QUOTE(daniel @ Sep 3 2006, 05:31 PM) [snapback]313709[/snapback]</div> Hmmm...I got that response once and the full article two other times...Gremlins? :blink:
if you want to see a glacial erratic, go to Okotoks Alberta,20 minutes south of Calgary and ask any local how to get there. 100' long 60' wide 40' tall left behind when the glacier melted. Used to be another one just north of Calgary but it's in a subdivision now and I couldn't find it again.
<div class='quotetop'>QUOTE(Tideland Prius @ Sep 3 2006, 10:58 PM) [snapback]313839[/snapback]</div> Thanks. Not sure if my link worked so I'll try again. http://www.flickr.com/photos/35361906@N00/show/
