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I've been playing Worldle for a while, and noticed that colder countries seem to have more rugged coasts. See Svalbard for example:

And Patagonia:

Whereas e.g. Bali is smoother:

Does it have something to do with the ocean being stronger in colder climates and washing away more of the "softer" parts of the coast over time? That's just a layman's guess, I'm really not sure.

Excited to learn about this if anyone knows the answer!

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    $\begingroup$ Please have a look at the French Western Coast, or at the North Sea Coast, or at the Hudson Bay. "Smooth" shores, in rather harsh climates. Also check out Baya California, or Greece, or the Philippines. "Rough" shores in (sub-)tropical climates. Next step: Compare geology & elevation. $\endgroup$
    – Erik
    Jul 18, 2022 at 9:36
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    $\begingroup$ Ice -> fjords -> rugged coastline. See this related question: earthscience.stackexchange.com/q/23964/18081 $\endgroup$ Jul 18, 2022 at 11:41
  • $\begingroup$ Most obviously, might it be that in warmer climbs the shore has been battered only by water and in those colder zones, by ice? Even when only water is battering the shore, the main tidal influence of the moon changes as we move further from the equator, as does the temperature difference between land and water. Quite possibly irrelevant in human generations, but coastlines are formed over millennia. $\endgroup$ Jul 18, 2022 at 21:34
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    $\begingroup$ Is it that glaciers at some point in history are more likely in colder areas? $\endgroup$
    – komodosp
    Jul 19, 2022 at 9:12

2 Answers 2

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As Fred's answer and some comments wrote, this is of course not so generally true.

What is true is that many rough coasts were formed by past glaciation. Obviously you don't tend to get many glaciers near sea level in tropical regions, so that's part of the answer!

But it's not only about temperature. A more precise statement is: Cold, humid winters cause rough coastlines. Why? because the rapid accumulation of snow and then ice causes thick glaciers that flow relatively fast, even without much initial elevation. And flowing glaciers are mighty roughness-shapers, both by eroding high ground and carving out fjords, as well as piling up moraines. Scandinavia is a prime example: lots of humid atlantic air snows down over Norway, where the glaciers have carved out all those fjords. In the past they also reached over Sweden, where the coast is by no means mountainous but nevertheless quite rough, because the leftover moraines funneled more recent water erosion into irregular shapes.

By contrast, cold climates with less snowfall (e.g. Antarctica) rather glaciate slowly in flat sheets that steadily drift into the sea, and don't cause the above features as much.

And of course rough coasts can also be formed my mechanisms unrelated to glaciation, such as volcanism and particular kinds of stratigraphy, which may be found in warm climates.

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  • $\begingroup$ Can you say that freeze thaw has some influence on the rate of erosion? $\endgroup$
    – D Duck
    Jul 20, 2022 at 23:23
  • $\begingroup$ @DDuck I thought about this. Frost weathering is no doubt a significant part of erosion in some climates, but this should rather counteract the roughness-shaping effects, by systematically eroding exposed rock. On the other hand, glacial flow and erosion is probably also accelerated by partial thawing during summer. $\endgroup$ Jul 21, 2022 at 8:08
  • $\begingroup$ an interesting point that sounds plausible both ways $\endgroup$
    – D Duck
    Jul 21, 2022 at 8:19
  • $\begingroup$ This open access paper might be of interest Fractal properties of shoreline changes on a storm-exposed island nature.com/articles/s41598-017-08924-9 $\endgroup$
    – D Duck
    Jul 21, 2022 at 8:31
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Have you had a look at the northern coast of Russia or Alaska, in the cold Arctic? Having just looked at them on Google Earth, they are lengthy and seem very "un-rugged".

The northern coast of Russia:

Russia

The northern coast of Alaska:

Alaska

Opposite of that, in the hot subtropical Australia, the Kimberley coast in the north western part of the continent looks rugged:

Kimberley Australia

enter image description here

There's also the countries of the Aegean Sea, which have a very Mediterranean climate.

Aegean Sea

And there are also parts of the coasts of Myanmar, The Philippines, Indonesia and Fjordland in New Zealand which could be considered rugged.

To have a rugged coastline the coastline needs to be composed of rocky terrain, with valleys, gullies, canyons or mountains, that erodes slowly.

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    $\begingroup$ Fjordland in New Zealand has a colder climate. $\endgroup$
    – gerrit
    Jul 18, 2022 at 14:09
  • $\begingroup$ Kauai and Molokai in Hawaii also have some of the largest sea cliffs in the world. $\endgroup$ Jul 18, 2022 at 17:39
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    $\begingroup$ @gerrit: Wikipedia states "Fiordland temperate forests". The latitude of Fjordland is 45 S. Two sources from NZ 1 & 2 state summer temps of 17-22 C & 10-18 C with winter temps of 10-14 C and 1-9 C. Granted, its not tropical or Mediterranean & winter can be cold, but summer isn't. $\endgroup$
    – Fred
    Jul 18, 2022 at 17:49
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    $\begingroup$ What matters is not the climate now, it's the climate when Fjordland was formed, i.e., was it glaciated or not. $\endgroup$ Jul 19, 2022 at 6:00
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    $\begingroup$ You have a few counter examples, but when you zoom out a bit, it is noticeable that in the majority - colder areas appear more rugged than the warmer. Look at the west coast of America - Alaska, Canada and south Chile are rugged while it's relatively smooth from mainland USA down to the middle of Chile. North West Europe is rugged while from Spain down through Africa the coast is relatively smooth. There doesn't seem to so much jagged terrain in the warmer areas. $\endgroup$
    – komodosp
    Jul 19, 2022 at 9:08

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