I know parrot fish eat coral and poop out beach sand. However, as time goes by, if the parrot fish population decreases, the amount of sand on the beach gets washed away.
However, I have also heard that deserts are expanding. I assume that parrot fish don’t poop in the desert (but if they did, would anybody smell it?) so where does desert sand come from?
Also, why isn’t trucking sand from the desert to the beach a good idea? It seems like if the beach is deteriorating (a bad thing) and the desert is expanding (a bad thing,) wouldn’t doing this kill two birds with one stone?
Beach erosion doesn’t happen because they “run out” of sand. It’s a natural process, where sand is carried to and from a beach by ocean currents. Now, human construction projects will disrupt that sand migration – breakwaters in particular will collect “upstream” sand, blocking its movement “downstream”. The common effect is that beaches on one side of a breakwater will grow, while beaches on the other side are eroding. And beach erosion is only a problem because we develop beachfront property and expect it to stay that way.
Desertification, on the other hand, doesn’t happen because deserts are producing and spreading new sand. For the most part it’s due to human land misuse. Overgrazing and poor agricultural practices can destroy the flora that’s holding the desert back. The “new” desert sand was part of the soil previously, but once the plants are gone the organic components of the soil dry up and blow away, leaving only sand and desert behind. Removing sand won’t stop desertification.
With regard to the OP – Beach sand and beach sand aren’t even the same thing. The sand on the beaches here in Masachusetts and New Hampshire has a wholly different character from the beach sand in my native New Jersey. And the sand at Manchester Beach “sings”, unlike the other beach sand in the state. And none of these are like the coral sands down in the Caribbean. Or like the Lava Sands in Hawaii. Or a zillion other beach sands.
Sand is different, all over the world.
In one of his columns for “Rolling Stone” in covering the “Desert Storm” war in 1991, P J O’Rourke says while visiting the troops, he joked “at least you have plenty of sand available to fill sandbags”. One of the troops told him no, that sand was different and they had to import sand to fill sandbags. Seems fishy to me but I wasn’t over there.
Going along with what Cal points out, sand is not itself a mineral, but a range of coarseness. Most people can easily detect the difference between boulders and ‘normal rocks’ (technical term cobbles) and them from gravel. Sand is the next range down, from 2 mm to 1/16 mm in diameter, feeling gritty to the touch, as opposed to silt, the next finer range, which feels powdery to the touch. Just asa boulder can be made of basalt, granite, sandstone, limestone, etc., so can sand. Most sand, inland and on temperate and frigid-zone coasts, is predominantly silica, mostly quartz, since it’s the most common mineral sufficiently resistant to weathering to be ground down only to sand consistency, as opposed to finer silts and clays. Tropical and subtropical beaches, on the other hand, are characterized by bright white sand which is derived from limestone.
Many (most?) deserts don’t have the iconic big dunes made out of loose sand, and actually have extremely hard-packed soil. In some deserts the sand is practically cemented together. I don’t know the exact case in Iraq, but I wouldn’t be surprised if there were large areas of the country where the sand was hard enough that you couldn’t dig it up by hand.
It could be the same thing because beach sand is often imported from areas with better quality sand. I don’t know if desert sand is ever used that way. In the cases I know of, the sand is moved from one beach to another. I believe some of Hawaii’s beaches have sand from California. It is probably much more economical to gather sand on barges for transport from the shore, instead of carrying it out of a desert.
I was going to mention this. I know how hot the sand seems on some beaches–at White Sands, the gypsum sands are cool on your feet even though the air temp might be over 100 degrees. A wonderful place!
To give an idea of the scale involved, assume your beach is just 1 mile long, 50 yards wide and you want to add 1 yard of sand.
That’s 88,000 cubic yards of sand weighing around 120,000 tonnes.
Which could all get washed away in a season if the prevailing currents were against you.
Sometimes they are - the Sahara Desert gets a significant input blowing in from the West coast of Mauritania - you can observe the effect from satellite photos:
There’s more than one desert that goes right to the sea (for instance, the Skeleton Coast of the Namib) - those’d be the same. But in general, beach sand is eroded differently than desert sand, hydraulic erosion produces different microstructures on the grains from aeolian ones. It gets so you can tell in a sandstone whether it was a desert dune or a sandbar (this is in addition to the many macrostructures you can use to tell the same thing)
Just for the record, “expanding desert” does not imply “more sand in desert.” Many deserts have no sand at all. As an example, I used to have a small ranch in a desert. I had about 30 acres of it planted in alfalfa, all of which was watered from a nearby river. The soil was excellent, and no sand for miles around. We got about 7-8" of precipitation per year.
Your reply to my statement doesn’t seem to follow. I point out that beach sand varies from place to place, clearly implying that “beach sand” itself doesn’t identify a sand type, and you reply that the Sahara Desert gets (presumably) beach sand from Mauritania.
Your reply might make sense if I said that desert sand isn’t the same as beach sand, but it seems pointless in this case.
Beach sand can, of course, be the same as beach sand elsewhere – the sand at Point Pleasant, NJ is pretty much the same as the sand at Atlantic City, NJ. And desert sand from one place can be the same as desert sand from somewhere else. But just getting two samples of sand from beaches won’t guarantee that they’re at all alike.
This is interesting. Would a layperson be able to tell the difference between beach sand and desert sand? Could I be sitting on the beach somewhere, running my toes through the sand and suddenly sit bolt upright and be all, “WTF!? This is DESERT sand!!”
I suspect a possible lack of salt and maybe silica as well would seperate the two. Is desert sand usually ancient ocean sand or is it more decomposed organic matter? I also understand that I may be totally misusing some terms in the last sentence.
No. The differences are microscopic, and statistical, not directly visible on any individual grain. You’d need an SEM. IIRC, it’s something about surface scratch patterns and degrees of rounding/faceting, but it’s been years since I read the article.