Wednesday, February 10, 2016

Search Challenge (2/10/16): Why an arc of lakes?


You know that odd sensation you get... 

... when you first notice something that you should have seen before now?  

I mean, sometimes you'll look at something you've seen for years, and then a new feature just sort of pops out at you.  

Ever have that happen to you? 

It happened to me recently when I was looking at a map of North America.  We've all seen this about a zillion times, and yet, this time, I saw something different.  Here's the map as we usually see it: 

From Google Maps. The blue dot in California shows you where I am. 

And THIS time, it struck me that there's a big line of big lakes stretching across Canada and into the US.  Here's another way to look at it that makes the arc of lakes very clear: 


Here's another version of the same map.  (I've labeled some of the lakes to save you a couple of minutes of searching.)  

Image from Google Earth, with my annotations of the major lakes on this arc.

See that?  Although I've looked at maps of North America just about my entire life, I'd never noticed that the lakes line up so neatly. This striking observation leads to today's Search Challenge. 

1.  Is this arc of lakes across the top of North America just an accident of geography?  Or is this actually the consequence of some gigantic geological process?  

I suspect I know the answer to this, but I'm going to enjoy the search process along with you. 

The Search Challenge here is "how do you look for something like this?"  If you're not already a geologist, how can you find out enough about the topic to ask a reasonable question of Google?  

Let us know your answer... and your process (including the most useless time sink diversions that take you off the path to the answer)!  

I'll be reading the comment stream this week, and will chime in from time to time.  

This will be fun.  

Search on! 


9 comments:

  1. Good day, Dr. Russell and everyone.

    Yes, it is fun and new words, knowledge and tools. I also noticed the new labels at the end of the post, those are helpful.

    Searched:

    Tried your labeled image adding [USA lakes Canada connections ]

    About 14,000 years ago, the Great Lakes area was covered with a glacier that was more than a half-mile (1 km) thick. As the glacier melted, it slowly moved toward Canada and left behind a series of large depressions that filled with water

    [great bear lake manitoba ontario connection]

    Prehistoric geology;Great Bear Lake lies between two major physiographic regions Links to

    The physiographic regions of the world are a means of defining the Earth's landforms into distinct regions

    Lake McConnell covered parts of what are now the Great Bear Lake, Great Slave Lake and Lake Athabaska basins

    [physiographic lakes usa canada]

    Physiographic Regions of the US and Canada

    Lakes are in site where Canadian Shield joins Interior Plains

    Google suggest: [Canadian shield vs interior plains]

    [Canadian shield Usa interior plains lakes formation]

    Physiography originally meant "the study of natural phenomena," but later usage limited its application to physical geography in particular and, more recently, to landforms alone. Physiographic regionalization is defined here as the process by which regions with relatively homogeneous physical geography are determined.

    [Usa "interior plains" lakes]

    ["Canadian shield" United States "interior plains" division line name]

    PHYSICAL GEOGRAPHY OF THE US

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  2. Okay, this is search is fluid and ongoing but my early results are as followed:

    [north american line lakes]

    About four down was a question similar to yours found on Quora.com. Now, being a librarian, I'm not going to take this as an authoritative source BUT I wanted to at least take a peak at what people surmised.

    https://www.quora.com/Why-are-the-Major-Lakes-of-North-America-in-a-line

    There is a geologist of 35 years (if I am to believe that) that talks about the massive weight of a receding ice sheet leaving depressions in the earth, leaving the line of lakes. What was important to me, though, wasn't in this answer but in the one at the bottom, where a gentleman stated, "It was the direction in which the Wisconsin glaciation receded that caused them"

    AHA! Now I have a possible term to investigate "Wisconsin Glaciation".

    So, search I did for [Wisconsin glaciation]

    Lots of results and in-depth geological talk that I can't really understand but appears that this may be the cause.

    I did find this one hit (http://www.glaciers.pdx.edu/Projects/LearnAboutGlaciers/ROMO/BasicsIceAges.swf) that provides an interactive time line of the Wisconsin Glaciation and does show North America without the line of lakes and then the receding ice sheet leaving behind the lakes, around 12,000 years ago.

    I will search further but this lead seems promising.

    ReplyDelete
  3. "(including the most useless time sink diversions that take you off the path to the answer)! "
    okey dokey then……outside the arc, tangent side (outer annular bound), not secant (inner annular bound)… blue dot, in the detail…
    what lakes?
    detail, New Albion
    Drake
    Drake in CA
    sfgate - 17 different places - Point Reyes?
    The Golden Hinde - probably not a Disney cruise
    a Drake profile
    another Drake that altered the world timeline…
    …not this Drake - 461,569,147
    his own SE:
    for grins - search for Google…

    another Arc

    Great Bear Lake -
    eh, it's a Canada thing
    Viola Desmond
    LakePedia… who knew?
    Mackenzie River
    "The main inhabitants of the lake are the four-horned sculpin" - this one from Finland

    fwiw - the Princeton/brick pattern/P=NP image search doesn't work for me any longer - at least directly… takes an additional click now…
    brick pattern image search
    2nd click on image results
    P=NP additions —
    New Yorker
    Scott Aaronson blog
    Lily & Scott Aaronson colloquy…
    Scott & Lily
    about

    and the AZ cat has friends -
    ASU/Mercado katalt
    ASU/Mercado kataltalt
    a long, tortured history -
    ASU/Mercado
    Mercado history

    co-developers of the Mercado - Tohono connection Feb., 2 post:
    Tohono O'odham Nation.
    Fife Symington III - 2007, UFO sighting (might help explain the kitties)

    ReplyDelete
  4. I have a couple of great geology books where I first looked: Canada Rocks - the geologic journey and Four Billion Years and COunting. After spending the requisite 2 hours footling and reading curious stuff in these books the only pertinant thing I learned was the answer to Bob Dylan's question. It takes 200 million years to wash a mountain into the sea.

    So off to GS.

    [ great bear great slave athabasca arc ] finds a great map at https://en.wikipedia.org/wiki/File:Canada_geological_map.JPG

    and at http://ask.metafilter.com/201100/Why-are-there-big-lakes-along-the-edge-of-the-Canadian-Shield is our question answered but not very well. Too much guess work.

    So, on to googlebooks: The Ecology of River Systems edited by Bryan R. Davies, Keith F. Walker; where we find on 452 The "Great Lakes" of the Mackenzie darainage (Athabasca, Great Slave, and Great Bear are remnants of an arc of glacial lakes bordering the Precambrian Shield

    Great vid showing what the lower great lakes would look like when drained of all the water. Also explained is story of how they were formed. https://youtu.be/1lWeYa0_5bc For instance Superior blasted out by high pressure melt water.

    There is a lot of complicated geology involved, too involved for this forum. But for the "Great" lakes up north, the enormous mountain range known now as Grenville was eroded away over the 200 millions dumping enormous amount of sand westward which in turn was ground away at the edge of the remains of the Grenville Mountains by glacial actions leaving the lakes under discussion. Glaciers also ground away the "Great Lakes" in the south

    I had noticed this arc years ago but never thought to understand the 'why' til now. Thanks. This was great fun. jon

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  5. …meanwhile, the Hudson Bay Arc doesn't want to be left out - Canada has secrets…
    Nastapoka Arc
    Ken Jennings/Arc
    additional
    The Eastern Hudson Bay Arc
    impact?
    Hudson Pareidolia
    seeing & seeing
    Kamil/Egypt
    wiki - List of shields and cratons

    time sink from searching for bunny silhouettes/shapes… seemed like geological time…
    Beuys and pictures
    JB, only for the die hard 1/2
    2/2

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  6. My search process is a little sloppy. I did glom onto the term "arc" which you used in the description & that was very helpful in shortening my search. GEOL100 4-5-10 Historical Geology of North America Geologic provinces of North America http://www.geol.umd.edu/~jmerck/geol100/lectures/25.html ; Parks by Geologic Province http://geomaps.wr.usgs.gov/parks/province/index.html ; "geology of north american lakes arc" Google Search ; then -- http://www.geol.umd.edu/~jmerck/geol100/lectures/25.html ; then -- http://geomaps.wr.usgs.gov/parks/province/index.html ; then "glaciers lake formation north america" Google Search ; then -- http://seagrant.wisc.edu/home/Default.aspx?tabid=590 (super info re: U.S. Great Lakes) then -- https://www.asu.edu/courses/gph111/Glaciers/GreatLakesMovie5.swf ; then https://www.uwgb.edu/dutchs/planets/impact-No.htm = "One of the more ambitious suggestions around is that the arc of great lakes of North America might mark the rim of an impact basin. Actually, the lakes mark the zone of deepest excavation by the Laurentide Ice Sheet, which is typically about 300 kilometers in from the ice margin. Within the arc are innumerable lakes where the glaciers scoured down to crystalline bedrock. Hudson's Bay is centered in the arc because the ice was thickest there and the crust has not yet fully rebounded from the load." Sunday, November 15, 2015 1:38 AM "laurentide ice sheet excavation" Google Search -- http://www.geotimes.org/feb04/feature_Revisited.html

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  7. We found this answer at this site - https://www.uwgb.edu/dutchs/planets/impact-No.htm posted by a retired prof. of GeoScience at the Univ. of Wisconsin.
    "One of the more ambitious suggestions around is that the arc of great lakes of North America might mark the rim of an impact basin. Actually, the lakes mark the zone of deepest excavation by the Laurentide Ice Sheet, which is typically about 300 kilometers in from the ice margin. Within the arc are innumerable lakes where the glaciers scoured down to crystalline bedrock. Hudson's Bay is centered in the arc because the ice was thickest there and the crust has not yet fully rebounded from the load."

    It took quite a few tries for us to find this. We first went to the USGS site and did a search for and got an article entitled "Extent of Pleistocene Lakes in Western Great Basin" Thought that that may give some information but turned out it wasn't the correct area. Then we went to Google and searched for Ar
    We went back to the posted map and saw the names of the lakes so we did a search for < formation "great bear lake" "great lake" "great lakes" :lake winnipeg" and one of the results was a you tube videa called "you know 5 Great Lakes but in rEality there are 9" The video wasn't that good except at the very end it mentioned the great north american hudson crater zone. So we did a search using those terms which led us to the result above. School is ending now for our short mid-winter break so we probably won't get back to do any more investigating.

    ReplyDelete