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Thread: Strange Boulders in the Lake Louise Area

  1. #1

    Default Strange Boulders in the Lake Louise Area

    I wasn't sure where to write this question so if I put it in the wrong place and a moderator can move it to the right place, by all means be my guest. Just please send me an indication where you moved it to if you do.

    I have been doing some snow machining in the Lake Louise area this winter and I have discovered some very large, unusual boulders located in the middle of nowhere that probably weigh close to a 100 tons. My question is, how did they get there? I am not a geologist but I do study geology a little bit as a hobby. I am aware of glacial erratic boulders located throughout the Matanuska-Susitna Valley that were deposited directly from the Naptowne glacier, but I was under the impression that the Lake Louise area was once under water due to an extremely large glacial lake known as glacial lake Ahtna. Supposedly this lake was as big or bigger than some of the great lakes of the midwest (lakes Michigan, Superior, Huron, Ontario, Erie etc.). So my question is, what force could be responsible for depositing these large boulders in the Lake Louise area? Were they deposited by glaciers before Lake Ahtna formed? If so, why are they not buried by lake sediments? Were they possibly carried by chunks of ice that broke off from the terminus of the glaciers surrounding Lake Ahtna? I'm not looking for 101 opinions. I'm actually wondering if anyone on here has actually studied the geology of this region in detail and if they can explain it to me in laymen's terms. Thanks.

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    webmaster Michael Strahan's Avatar
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    Here you go-

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    Quote Originally Posted by Michael Strahan View Post
    Here you go-

    You watch too much TV Mike. I thought I said I'm not looking for 101 opinions. I was actually looking for a real explanation. But funny. Good response.

    On another note. Just in case someone might be wondering why I even care. #1, I actually find geology interesting. #2 even more important is if one of my kids or grandkids someday asks me, "Hey Papa, how did that big boulder get there?" I would like to give them an intelligent response other than "Gee, maybe a rock giant threw it here".

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    Giant Icebergs in the lake dropping them there. Or physically moved by a previous glacier before lake
    Ahtna

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    Default Strange Boulders in the Lake Louise Area

    If you look for a geologic map of your quadrangle it may shed light on this. Could be more recent quaternary deposits overlaying older lake Ahtna stuff who knows... Consulting the map would be my first route. Will also tell you ages of the bedrock of adjacent mtns. Good info.

    You want gulkana quad geologic map I am guessing, fyi. Unless you are further to the west which would be talketna mtns.

    DGGS has the maps. Let me know if you have questions interpreting them

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    Supporting Member iofthetaiga's Avatar
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    I believe the Basin was glaciated several times throughout the Pleistocene, before, during, and after the the presence of the lake. Glacial erratics is my vote.
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    Member cod's Avatar
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    I was up to Louise with my brother (the astronomer, geologist, biologist, etc etc. ) a couple wkends ago on our snogos. He got to telling me about the great lake Ahtna and how it filled the entire copper basin. He went on to explain that when the lake went out the massive ice sheets roared down and out the valley carrying these boulders riding on top the ice. Some of the ice shelves broke up and/or rolled depositing these massive boulders throughout the entire basin.
    Makes sense to me.
    Your sarcasm is way, waaaayyyyyyyy more sarcastic than mine!

  8. #8

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    Quote Originally Posted by andweav View Post
    If you look for a geologic map of your quadrangle it may shed light on this. Could be more recent quaternary deposits overlaying older lake Ahtna stuff who knows... Consulting the map would be my first route. Will also tell you ages of the bedrock of adjacent mtns. Good info.

    You want gulkana quad geologic map I am guessing, fyi. Unless you are further to the west which would be talketna mtns.

    DGGS has the maps. Let me know if you have questions interpreting them
    Yeah, thanks Andweave. I actually did look at some of the geologic maps online. Unfortunately they are a little vague and open to interpretation. But thanks for the tips.

    Quote Originally Posted by iofthetaiga View Post
    I believe the Basin was glaciated several times throughout the Pleistocene, before, during, and after the the presence of the lake. Glacial erratics is my vote.
    Yeah, that is what I was kind of thinking too. Although my assumption would be that if the glacial erratic was deposited prior to the formation of Lake Ahtna, that the erratic would be deposited in lake silt. But thanks for your input.

    Quote Originally Posted by cod View Post
    I was up to Louise with my brother (the astronomer, geologist, biologist, etc etc. ) a couple wkends ago on our snogos. He got to telling me about the great lake Ahtna and how it filled the entire copper basin. He went on to explain that when the lake went out the massive ice sheets roared down and out the valley carrying these boulders riding on top the ice. Some of the ice shelves broke up and/or rolled depositing these massive boulders throughout the entire basin.
    Makes sense to me.
    Interesting about the boulders floating in ice. If that is true I wonder why they deposited in the bottom of the lake and not where the lake drained into (such as the Matanuska Valley)

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    Member cod's Avatar
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    Quote Originally Posted by Bushwhack Jack View Post
    Interesting about the boulders floating in ice. If that is true I wonder why they deposited in the bottom of the lake and not where the lake drained into (such as the Matanuska Valley)
    As we returned to town he pointed out the lake shore line that still exists along the mountain side in the eureka valley. (Look across the valley in the tower area). The lake did not drain towards the Mat Su. It totally and quickly drained out the copper river delta. Thus the large delta that exists today. This event of draining was a rapid happening. Massive ice sheets ground against mountainsides picking up small boulders the size of trucks as they rubbed thru valleys. Truck sized boulders were nothing compared to the massive movements that were taking place.
    There are several places that one can still see the shoreline delineation marks on various mountainsides even across the Copper river against the Drum, Sanford, etc mountainside.
    ( the shorelines show as distinct horizontal indications part ways up the mt sides. There is a distinction between vegitation and rock formation and strata. )
    Your sarcasm is way, waaaayyyyyyyy more sarcastic than mine!

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    Supporting Member iofthetaiga's Avatar
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    Quote Originally Posted by Bushwhack Jack View Post
    Yeah, that is what I was kind of thinking too. Although my assumption would be that if the glacial erratic was deposited prior to the formation of Lake Ahtna, that the erratic would be deposited in lake silt. But thanks for your input.
    As I implied, I believe (perhaps I'm wrong) that there was at least one period of glaciation after the lake went out. Thus glacial erratics not buried in lake silt.
    ...he who knows nothing is nearer to truth than he whose mind is filled with falsehoods & errors. ~Thomas Jefferson
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  11. #11

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    Quote Originally Posted by cod View Post
    As we returned to town he pointed out the lake shore line that still exists along the mountain side in the eureka valley. (Look across the valley in the tower area). The lake did not drain towards the Mat Su. It totally and quickly drained out the copper river delta. Thus the large delta that exists today. This event of draining was a rapid happening. Massive ice sheets ground against mountainsides picking up small boulders the size of trucks as they rubbed thru valleys. Truck sized boulders were nothing compared to the massive movements that were taking place.
    There are several places that one can still see the shoreline delineation marks on various mountainsides even across the Copper river against the Drum, Sanford, etc mountainside.
    ( the shorelines show as distinct horizontal indications part ways up the mt sides. There is a distinction between vegitation and rock formation and strata. )
    That's interesting. I am familiar with the area you are talking about in Eureka Valley. Like mile 120-130 area on the Glenn. I do recall reading about the Lake Ahtna draining at least once in the Mat-Su valley. See link. Perhaps it drained in multiple places.

    http://www.livescience.com/9904-anci...landscape.html


    Quote Originally Posted by iofthetaiga View Post
    As I implied, I believe (perhaps I'm wrong) that there was at least one period of glaciation after the lake went out. Thus glacial erratics not buried in lake silt.
    Makes sense, and it is as good of an explanation as any other. Thanks to you both for your insight.

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    Member cod's Avatar
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    Quote Originally Posted by Bushwhack Jack View Post
    That's interesting. I am familiar with the area you are talking about in Eureka Valley. Like mile 120-130 area on the Glenn. I do recall reading about the Lake Ahtna draining at least once in the Mat-Su valley. See link. Perhaps it drained in multiple places.
    http://www.livescience.com/9904-anci...landscape.html
    Interesting article. I always understood Ahtna Lake to be over the Copper River basin.
    Clearly the landscape (the fact that there is a 'pass' between Copper river watershed vs Mat Su watersheds) that now separate the two would prevent the flow of the one watershed from affecting the other watershed.
    Perhaps however, the Lake may have overlapped both watersheds.
    My brother is close friends with a fella that did geological work throughout the basin in which he found these giant boulders, chiseled off pieces and was able to match the pieces with various Mt ranges in the areas. I guess this fella took samples from about every mt around the basin.
    Your sarcasm is way, waaaayyyyyyyy more sarcastic than mine!

  13. #13

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    If you google earth the Houston area, like visnaw lake and such, and notice the gravel mounds are chevron shaped, due to a massive flood from that lake. I have always heard the lake filled and drained 3 times, and for the boulders maybe they were uncovered when the lake went out due to all the water rushing around.

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    Quote Originally Posted by fishhook57 View Post
    and for the boulders maybe they were uncovered when the lake went out due to all the water rushing around.
    Hmm, Maybe. Good idea.

  15. #15

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    Interesting Bushwack Jack. Where abouts did you see these big erratics? Here is a pic of my favorite erratics near Petersville: http://crust.outlookalaska.com/Blog/..._2013_pano.jpg

    GPS: https://www.google.com/maps/place/62...s0x0:0x0?hl=en

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    Quote Originally Posted by Dinglishna View Post
    Interesting Bushwack Jack. Where abouts did you see these big erratics? Here is a pic of my favorite erratics near Petersville: http://crust.outlookalaska.com/Blog/..._2013_pano.jpg

    GPS: https://www.google.com/maps/place/62...s0x0:0x0?hl=en
    Yeah, I've seen that boulder in your picture before off of Petersville road. That's a big one. There are more big boulders in the Lake Louise area but one in particular that I've had in mind was about 10 miles to the east of Lake Louise along a trail called the Big Rock Trail. There is a very big rock at one of the main junctions of that trail and it is enormous. It has to be glacial in origin, but it sits right smack dab in the middle of where Lake Ahtna once was. Like Fishook57 said, maybe it became exposed by erosion when the lake drained out. Or perhaps it was floating in an enormous iceberg like Cod had mentioned. Whatever brought it there must have been an epic catastrophe of some sort.

  17. #17

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    If erosion exposed the rock, it probably would have had to been placed there before the lake was created. The floating iceberg w/ boulder makes sense to me. Here is a picture of the Big Rock Trail, and Big Rock in the background: http://crust.outlookalaska.com/Skiin...4_P1020301.jpg

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    Quote Originally Posted by Dinglishna View Post
    Interesting Bushwack Jack. Where abouts did you see these big erratics? Here is a pic of my favorite erratics near Petersville: http://crust.outlookalaska.com/Blog/..._2013_pano.jpg

    GPS: https://www.google.com/maps/place/62...s0x0:0x0?hl=en
    That's awesome

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