Does the formation of sand on our coastlines follow the same process as sand in our inland deserts? And what is that process?
Finally is there more sand inland on this planet than on the coastlines world wide.
Sand is produced by basically the same processes of wind and water erosion on coasts and inland. Rocks are worn down to smaller and smaller sizes until it is reduced to sand grains (which may include single crystals from the original rock). Obviously wind erosion is going to dominate in deserts and wave erosion on coasts, but both factors contribute in both areas. Also, some of the sand in deserts may have been produced when those areas were marine, while some sand on coasts may have been blown in from elsewhere.
Sand is created by the erosion of rocks by rivers in the mountains as they run downstream to the sea. The river outlets into the sea are major sources of new sand along the coast.
Once there, the sand is carried downcurrent parallel to the coastline – northward along the Atlantic coast with the Gulf Stream; southward along the Pacific coast. (I’m referring to the North American coasts here.) This forms the beaches all along the coast.
Wherever there is an off-shore canyon (like Monterey Bay for example), the sand falls into the canyon as it passes by. Thus, on the Pacific coast, you’ll find beaches on the north side of off-shore canyons, but just south of canyons (as far as the next river outlet), there’s rather little sand and a lot of bare rock. Where the next river to the south opens into the sea, you’ll again find beaches stretching southward until the next canyon.
For the Atlantic coast, similarly, but moving northward.
Cite: I learned about this in an Intro Oceanography 101 class I took at University of Hawaii 30-some years ago.
I’m not a geologist, but–
the processes are similar, in that they both are both slow processes of erosion, where particles are constanly colliding and causing smaller particles.
At the coast, pounding wave action causes constant banging of rocks and sand particles. Most sand is basically crushed rock, but some is crushed seashells.
Inland, this can happen in creeks and rivers. Also wind blows sand and dust particles across rocks.
I don’t know how much inland sand comes from ancient seabeds.
If any sand experts do appear here, I hope they can discuss how sand seems to come in clumps of similar sand, even on a beach with lots of different sand. By this I mean how you will see patches of coarse sand amidst regions of finer sand. I think like particles prefer to stick to like particles, based on shape and/or chemistry, but I’m not sure.
Edit: Wow, a lot of sand experts showed up while I was typing!
Senegoid’s post implies that I’m wrong about the wave thing, so forget that.
I guess most sand originally comes from streams and rivers.
Well, when most people say “sand”, they are thinking “tiny bits of quartz”, which is igneous. That igneous rock is uplifted into mountain ranges, eroded into sand by rain and rivers, and washed into oceans, where it forms into sandstones. The ocean beds are eventually uplifted, eroded again, and become sand again.
(That, of course, is simplifying things greatly.)
When you say “coastlines”, do you mean “beaches”, or are you including offshore sand?
Many sand beaches (especially white ones) are fish poop. Most famously the parrot fish.
Given that the area of the interiors of continents is so much larger than the continents, it’s no doubt true that most sand is produced by erosion by rivers and wind in inland areas.
However, waves also cause erosion on rocky shores, so some sand is produced there. This is especially true on islands.
I’m pretty sure that scientifically speaking anything that gets in your bathing suit and makes you feel uncomfortable is sand. It’s science people, just ask Anakin:
Yes. That raises a good point.
Given that we’ve established that most sand comes from rivers (with some probably not insignificant contribution from ocean waves and fish poop), whence all the sand on Tatooine and Arrakis? Did they hire the Trade Federation and the Shipping Guild to bring it all in?
Most sand on Earth comes from water erosion just because Earth has a lot of water. But wind is perfectly capable of eroding rocks into sand. Mars contains lots of sand even though it has virtually no water (now).
Let us remember that a lot of shoreline sand was imported from other places to make nice looking beaches. And in the funny facts department, a lot of sand is exported from other places to the Middle East, including Saudi Arabia. It’s a heavily used construction material, and used for sand-blasting as well, and particular compositions and particle sizes are necessary and not always available in desert regions.
I could answer that, but I’m not going to be nerd-sniped.
Are you talking about the volume vs. surface area thing, or are you suggesting TARDIS continents?
The second “continents” should be “coasts,” of course.
It’s a mistake to think water-based erosion only happens on continents or their immediate coasts. Turbidity currents can be quite erosive. And volumetrically, they’re the largest sediment transport mechanism worldwide, so probably the biggest eroder, too.
True of course, in some places where they do that. But note that this is an on-going process. The sand they import to make a nice beach doesn’t necessarily stay put. Along with sand from any other source (rivers, or wave erosion against the coastal rocks), the ocean currents eventually wash the sand away, moving it downcurrent until the sand falls into the next canyon, leaving mostly bare rock behind where the beaches were.
What’s different about the sand coming down from rivers, is that there’s a steady on-going supply of new sand to maintain the nearby down-current beaches.
I wouldn’t expect different types of sand to prefer to stick to each other.
What is probably happening is a combination of
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All of the grains in a small patch of sand probably came from about the same place, so they’re likely to be similar; and
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As grains of sand (and smaller stuff, too) move through the water, bigger (heavier) ones tend to settle faster, so the result is that the big rocks fall out in one spot, and the smaller ones somewhere else (and the silt ends up in a different place). So when sand washes onto a beach, it’s going to be somewhat sorted by size.