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Normal seashores are curved.

On a planet with earthlike features, the seashores are entirely straight. For example,

.

Long paths of straightness extend for many miles at a time. Note that these seashores aren’t hexagonal or ordered, they’re random.

What geographic processes could result in such bizarre seashores? And not only a few of them, an entire planet of them?

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    $\begingroup$ Does your planet have to have a moon to fall under your definition of Earth like? Much of the curvature of beaches comes from years of tidal based erosion - whatever allows them to exist to begin with, I think no to low tidal forces would be required to keep it. $\endgroup$
    – user97385
    Commented Jul 30, 2022 at 21:48
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    $\begingroup$ Worth remembering that "a region of an otherwise normal planet has naturally developed these features" is an awful lot easier to arrange than "every part of this entire planet has geological formations that are either rare or absent on other planets". $\endgroup$
    – Starfish Prime
    Commented Jul 31, 2022 at 14:29
  • $\begingroup$ I'd argue it isn't really possible on a planet-wide scale. The reason beaches and shore lines form the way they do is purely a matter of physics and entropy. This is so engrained into how the world forms that we even call the rounding of things "sanding down". Sure we have specific land formations in specific locations under specific conditions that simply don't exist planet-wide. Even those places look just as rounded as soon as you get any serious altitude. $\endgroup$
    – TitaniumTurtle
    Commented Jul 31, 2022 at 19:43
  • $\begingroup$ @Glorfindel I don’t think a source is necessary. ibb.co is an image hosting site and I created the image myself. $\endgroup$
    – joyoforigami
    Commented Feb 9, 2023 at 4:58
  • $\begingroup$ You're right, feel free to remove it. My script that repairs images tries to be on the safe side and provides attribution; for some image hosters it uses an HTML comment instead. I'll add ibb.co to the list, thanks! $\endgroup$
    – Glorfindel
    Commented Feb 9, 2023 at 7:45

3 Answers 3

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There are perhaps 2 methods that can achieve what you are looking for depending on the scale of your jagged edges.

Sedimentary layer shifting, collapse and erosion

It is conceivable that a sedimentary area has over time become eroded and the layer angle shifted to produce straight edges over dozens of metres. This is evident at Mistaken Point, Canada. As the strata layers have different properties and formed over different eras of time, the layers are straight. As time progresses, they shift and erode, exposing the layers to water forming straight edges.

enter image description here

enter image description here

Earthquake faults

Like at the Pupatea Fault, New Zealand, where a magnitude 7.8 quake caused a seismic shift and exposed along the shore a roughly km long straight edge. This is rare and relies on a geologically consistent layer to form, but nonetheless creates a permanent face in the rock which could be, over time, a jagged straight shoreline.

enter image description here

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Artificial.

emmeloord

Depicted: Emmeloord which is built on a polder - lands taken from the sea. The resulting engineered shorelines are straight because of the convenience of building in straight lines.

The Dutch are famous for this and these are the long straight lines requested from the OP. But the Dutch do not have a monopoly on this. Here are similar obviously artificial shoreline from Tokyo. Some of these are reclaimed lands and some were made to facilitate human use.

tokyo

These artificial straight line shores are not some sort of fractal. To my eye they seem pretty random. It is not such a stretch to think that a planet inhabited by intelligences not unlike us might similarly engineer their shorelines.

They will not stay straight without maintenance. If they are not maintained the water will wear them into nonlinear shapes again. Unless the water also disappears. I found this city on what used to be the shore of the Aral sea.

aral sea

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I am going to suggest an earthquake faulting action with basically a stone sea-short. This ought to be able to give long fairly straight sections. You had an entire region above the waterline then the quake hit and some large pieces simply sank beneath the waves.

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    $\begingroup$ @SoronelHaetir - I was thinking about that too, and then thought I should be able to find some. No luck. You? If so, link it up! $\endgroup$
    – Willk
    Commented Jul 30, 2022 at 22:29
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    $\begingroup$ I am blind, so finding an example of such would be fairly difficult for me. $\endgroup$
    – SoronelHaetir
    Commented Jul 31, 2022 at 0:18
  • $\begingroup$ @AngryMuppet I think it’s a typo… $\endgroup$
    – joyoforigami
    Commented Jul 31, 2022 at 0:24

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