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I saw this interesting graphic (The World’s 25 Largest Lakes, Side by Side) of some of the largest lakes in the world.

It strikes me as somewhat curious that most of the lakes have a high eccentricity - that is, they appear to have a "length" at least three times more than a "width". An exception in the image may be Lake Victoria, which has a somewhat circular shape.

Is this observation a coincidence, a conclusion based on too small a sample size, or could this be related to how the lakes were formed?

I'd guess that Erie and Michigan were formed roughly at the same time - both have a high degree of eccentricity, but Michigan is oriented more north-south while Erie is diagonally oriented to the northeast.

Naively I would expect lake formation to be mostly isotropic - leading to circular shapes.

The question was born out of curiosity. This conflicted a little with my intuition - for example many features on Earth, such as tectonic plates or many large islands such as Hokkaido or Madagascar, have very "Schmoo" shapes, so my first guess would be "why not lakes?" I also recall the dictum that "nature abhors straight lines" - but Loch Ness is pretty straight.

Nonetheless I recall or guess that many lakes such as the (North American) Great Lakes were formed from the recession of glaciers. The Wikipedia article lists many different kinds of lakes - most of those do have some eccentricity. It's perhaps somewhat interesting that many of the processes of forming lakes are associated with high eccentricity.

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  • $\begingroup$ what research have you done before asking this question.i ask because there is no need to repeat the things you know from reading about the formation of lakes and rivers in an answer to this. $\endgroup$ May 20 at 3:03
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    $\begingroup$ It depends on the type of lakes you are looking at (i.e., it depends on the formation process of the lake). For instance, glacial lakes tend to be very elliptical, because glacier tongues carve long valleys that are then filled with water. If you look at this list of lakes from the Lake District (England), you can definitely see that. On the other hand, maar lakes tend to be very circular, because they are formed by a volcanic explosion which leaves a round hole in the ground. $\endgroup$ May 20 at 7:50
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    $\begingroup$ As for the African Great Lakes (Malawi, Turkana, Tanganyika), they were formed along the East African Rift, so it makes sense that they are elliptical. $\endgroup$ May 20 at 7:56
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    $\begingroup$ Most lakes will have formed as part of active drainage systems, with streams and rivers flowing into and out of the lake, so elongate forms are a natural part of their formation. Unless a circular lake is endorheic (a closed basin with no outlet other than evaporation) it is likely to evolve into an elongate form as the stream systems feeding and draining the lake erode. $\endgroup$
    – Andy M
    May 20 at 11:16

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I can think of six main types of lake regimes based on the environment in which they form and exist (this is a generalisation). In the comments to the question it is mentioned lakes in formerly glaciated areas and lakes formed by tectonic activity such as the African rift. A more rare and perhaps spectacular form come from meteorite impacts. To those I would add lakes related to volcanism, lakes formed in karst terrain and thermokarst lakes formed in permafrost and glacial environments.

Glacially formed lakes are caused by either excavation of valleys to form troughs in which lakes form or by damming of water from glacial deposits. In the case of troughs they definitely are highly eccentric to use the terminology of the question. However, lakes dammed by glacial deposits may have various shapes depending on the terrain upstream of the damming. The damming may of course occur in valleys which again results in eccentric lakes. But local topography will in the end determine the lake fom.

Lakes caused by tectonic activity, such as in the extensional regime of the African rift will be laterally constrained by the rift walls and thus primarily also eccentric. Again, it will be the shape of the terrain that decides the shape so with linear tectonic land forms lakes will probably tend to be eccentric.

Volcanic lakes, on the other hand, probably tend to be more circular in shape since they form in calderas, maars or volcanic craters, all of which are more circular shapes. Some examples include Mono Lake (USA), Pulvermaar (Germany) and Laguna de Quiltoa (Ecuador).

In karst terrain lakes may form from collapse of caves forming water filled sink holes such as Crveno Jezero (Croatia). These are often more circular in shape due to the collapse structure.

The final environment is the cryospheric regions where frozen ground thaws and creates depressions that fill with water. The depressions largely grow radially due to the heat captured by the water of the lake "eating" into the sides of the lake. These types of lakes are common place in Alaska, northern Canada and northern Russia and easily found by a quick browse in Google Earth.

Impact craters form more or less circular lakes if they fill up with water such as Lonar Lake (India). However, sometimes the centre of the impact is uplifted leaving lakes that form a ring such as in the case of Lake Manicougan (Canada) and Lake Siljan (Sweden).

I am sure one could add more instances where lakes form but in general you need a depression formed either by erosion or tectonics or a damming caused either by deposition or, again, tectonics to form a lake.

So to sum up, the form of lakes depends on the environment in which they appear and the processes involved in shaping the topography. In the case of the comparison mentioned in the questions, the lakes presented (one sea) are all very large and may not be representative for all lakes in the world.

There is no strict definition as to the lower limit to what is considered a lake which makes it difficult to assess all the smaller lakes, particularly thermokarst lakes.

Use e.g. Google Earth to visit the sites mentioned in the text.

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    $\begingroup$ What a thorough, patient, and informative answer to a question asked out of idle curiosity! $\endgroup$
    – Mark S
    May 20 at 18:41

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