@Faintdreams My immediate reaction was "this is more geology than geography" because whether a beach is sand or pebble depends on the slope of the land as it meets the sea, which is itself a function of the geological history of the landmass in question, and especially of how long it has been adjacent to the water. So I did a little poking around. I'd be shocked if there were no pebble or cobblestone beaches in equatorial regions, but you are correct in saying that pebble beaches are more common in northern/southern climes. This is because of the previous ice age, which had both land and ocean locked up under glaciers until about twelve thousand years ago. So the coastlines of previously glaciated areas have had less time for erosion to work on the materials at water's edge. Basically, the older the landmass, the flatter it is likely to be. And the flatter the landmass, the more likely it is to have sand deposits along the coast, rather than pebble or cobblestone deposits.
@SallyStrange oooh thank you. That's a really good summary for someone like me with no real prior geology knowledge.
One additional question though, Jamaica - as far as I'm aware has mountains but also only has fine sand beaches - is this the exception to the elevation rule ?
Although I'm not sure if Jamaica became an island through land erosion/sea encroachment of a larger land mass or if it sprouted out of the sea due to volcanic activity .. ?
@Faintdreams I'm still learning about the geology of Jamaica but from what I understand it's a combination of those. 140+ million years ago*, there was no Jamaica because there was no ocean in between Europe/North America and Africa/South America. When that supercontinent started splitting apart, there was plenty of volcanic activity, and the rocks that formed from that are part of Jamaica, but part of it is also pieces of that old continent. So it is mountainous but also pretty old. And, a large part of the land there is made of limestone, which is highly erodible, so that may contribute to the preponderance of sand as well. Just speculating about that last part though.
*edited to correct myself: the supercontinent (Pangaea, which you may have heard of) existed 300 million years ago and its breakup lasted from 150 - 100 million years ago. I initially put that breakup at 50 million years ago, but I was getting the Pangaean breakup confused with the collision of the Caribbean plate with the north American plate which took place about 50 million years ago, and which really put Jamaica into something resembling its current form.
I love geology! Please continue with the questions if you have more.
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