Circular lakes

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Circular lakes arcylon 7/5/05 12:44 PM
Does anybody know what these circular lakes and depresions are? Maybe some kind of volcanic feature like maars?
Re: Circular lakes Kempster 7/5/05 12:53 PM
I would guess by meteors. I know this lake (view attachment) was created by a meteor.


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Re: Circular lakes lodi 7/5/05 3:44 PM
This is neither a volcanicnor a extraterrestric but a permafrost feature. . Information eg at http://www.ingentaconnect.com/content/nrc/cjes/2002/00000039/00000008/art00007. Hope that helps
Re: Circular lakes Hill 7/5/05 4:01 PM
Take a look at this recent post and linked story. Then take a look at this post which I recently made.
The two look similar, but may or may not have different causes.

And hey....welcome to the forums.
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Re: Circular lakes arcylon 7/6/05 4:48 AM
Hi everyone, thanks for your help,
I've found out that these features are known as Thermokarst Lakes, they are indeed a permafrost feature.

Cheers!
Re: Circular lakes jeremy502 7/6/05 5:55 AM
if you look closely, youll see more little "lakes" that arent filled with water, they dont look like craters, just little sunken bits.
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Re: Circular lakes DavidRayL 8/22/05 10:47 AM

Dude, I dont think a Meteor would be able to do that. its in the canadian shield, if a meteor hit it hard enough to cause a circumference like that... it be WAY deeper than it is... this lake is more like a ring not a huge hole.
Re: Circular lakes DavidRayL 8/22/05 10:52 AM
Nice!
Me and my dad were tryin to figure it out.
thanks,
Re: Circular lakes Furry_Phil 8/23/05 2:46 PM
Manicougan is indeed an impact structure. It is about 240 million years old and the reason for the ring shape is explained here.
You might also like to try my Impact Crater Tour here.
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Re: Circular lakes DavidRayL 9/2/05 12:58 AM
Wow. Thats jsut crazy! I really didnt thin kthat it could have been an impact site... Sooo.. are they saying that because of the shield being completely rock and the pressure underneath, the melted rock actually got pushed back to level with the surface?

thats baffling man...

thanks so much for the info...
and sorry if i sounded a bit rude.. all apologies.
DRL
Re: Circular lakes Sojourner 9/2/05 1:07 AM
Welcome
and yes Kemptser got it in one. They are indeed thermocast lakes caused by permafrost and we even
have them down here in Australia which indicates that the climatic conditions we have known in our
lifetime are not how it has always be. Interesting...
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Re: Circular lakes Hill 9/2/05 9:08 AM
Are the Austrailian lakes in this post the ones you are talking about?
Re: Circular lakes ElisaDay 9/2/05 11:08 AM
I recognized them too, but I've never seen them so big! They're usually called "pingos" and there are several types, and there are "palsas" too.
In the Netherlands we've got them too, from the last ice age, though they're tiny compared to these.
Re: Circular lakes . . as a geological structure __Master_ 9/4/05 11:01 AM
Hi, i'm spanish and I apologice, first at all, about my inglish, so ...

This circular lakes are just a common geological structure, (called "dolinas" in spanish ) it happend wher we have a soft layer of sand and a hard layer under it.
The hard layer may be quimikly erosioned ( karst ) and when it can't hold the sand on him, it fall off leaving a circular mark in the surface.

If the hard layer ara very erosionated it may contain water and, if the level of the water inside the rock is most elevate than the surface, it will ascend, and create a lake in the circular mark created before.

ufff. .. my inglish is really hard.. so I think that the information is right.. thanks.

you can see the image attached

Re: Circular lakes . . as a geological structure MrFocal 10/4/05 7:27 PM
That is a great explanation (the english notwithstanding) and for that
we thank you. Did your explanation contain a reason for why the result is circular, not square, not oval? Were these once eruption areas (hot springs)?
Re: Circular lakes . . as a geological structure geogmajorbrum 10/5/05 9:47 PM
Thermokarst features are rounded because the initial formation of the feature begins at a point rather than the whole feature being created at once. The thermokarst features in question were most likely formed by ice wedges in the permafrost. In the summer the permafrost may have softened enough for water to work its way into a crack in the permafrost, once winter rolled around the water in the crack froze and in turn made the hole in the permafrost larger. Once the process begins, every summer that is warm enough to melt the ice wedge and surrounding permafrost increases the size of the thermokarst feature, usually in a uniform circular pattern around the feature, unless the melting edge reaches a more resistant soil, rock, etc. which doesn't melt as easily. If you look close enough, there are features that aren't perfect circles because of resistance to melting, but no squares.
This is a Terrestrial Impact Crater 5457171 10/24/05 7:22 PM
Manicouagan, Quebec, Canada
The Manicouagan impact structure is one of the largest impact craters still preserved on the surface of the Earth. The prominent 70 kilometers (43 miles) diameter, ice-covered annular lake that fills a ring where impact-brecciated rock has been eroded by glaciation. The lake surrounds the more erosion-resistant melt sheet created by impact into metamorphic and igneous rock types. Shock metamorphic effects are abundant in the target rocks of the crater floor. Although the original rim has been removed, the distribution of shock metamorphic effects and morphological comparisons with other impact structures indicates an original rim diameter of approximately 100 kilometers (62 miles).
Location 51°23'N, 68°42'W
Age 212 +- 1 million years
Re: Circular lakes arcticornithophile 7/10/07 9:35 AM
More on those lakes - my suggestion is that they are kettle lakes.

Why circular? Imagine post-ice-retreat big blocks of ice left on flat ground - as they slowly melt they are subject to wind from all directions - and they have some drainage that carries silt away in small quantities. This is one of the flatest areas you can imagine, slowly rising from Foxe Basin by isostatic rebound. Look east for the old Cape Dominion, which is now reflected to the west. The lakes are very round and very shallow - about the depth of a tall human. They are inhabited by king eiders (bound for Greenland), long-tailed duck (many perhaps also Europe-bound), Pacific loons and the odd tundra swan. This area also has nesting Sabine's gulls.
Re: Circular lakes ElCangri 9/17/07 5:42 PM
here is a good explanation:

http://ougseurope.org/rockon/surface/thermokarst.asp

nice find!!!
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Re: Circular lakes Tomatriox 7/15/08 7:27 AM
It's a meteor crater. I'm from Quebec and I know some association that tries to conserve this monument. I'ts probably one of the oldest crater in the world.

www.soslevasseur.org
Re: Circular lakes arcticornithophile 2/18/11 6:15 PM
These are kettle lakes
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