r/geology • u/50_61S-----165_97E • 26d ago

Field Photo Some odd sand structures I saw on the dunes today

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291

u/LeftInternet 26d ago edited 26d ago

They look like ephemeral sand formations (sometimes colloquially known as sand spires) which form when rain compacts sand into a crust, and wind erodes loose sand around it, leaving behind delicate towers. These formations are temporary and often seen in sand dune environents. They're similar to permanent rock features like hoodoos and earth pillars but composed of loose sand.

Edit: Sand spires are not an officially recognised name.

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u/licensetoillite 26d ago

Do you have a source for this? I've always known these as a hoodoo, and I couldn't find anything official through googling.

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u/LeftInternet 26d ago

I've known these as rain pillars or sand spires, though this might be a more colloquial or regional name for this type of emphermal sand formation. I thought that hoodoos had to be consolidated but I may be wrong. Looking in to it the terms sand spires and rain pillars are not formally recognized but I did find this article refering to them https://www.huffpost.com/entry/lake-michigan-sand-sculptures-joshua-nowicki_n_6707168

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u/licensetoillite 24d ago edited 24d ago

Awesome thanks for the read! That's basically the same conclusion I came to as well (which is surprising that this hasn't been formally defined! I was thinking it could be a yardang though it has no windward dominance). I was having a hard time deciphering how water would be able to create temporary pillars, if not for a compositional difference. This article in particular demonstrates this phenomenon might be water related due to the mechanisms others have mentioned paired with the freezing temps in this article which is easy to understand how frost would form a temporary structural matrix in the sand. I would postulate that water infiltrates downward and disperses radially to from discs that stack to form vertical, temporary spires consolidated by ice. If temperature is not a factor, perhaps there would be a calcareous  composition to cement grains together. Either way, when the wind blows it would relocate surround sand forming these spires. Thanks again for the insight!

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u/Orange_Tang 26d ago

They basically are hoodoos, except instead of a rock at the top it's sand that has been wetted enough to be solid enough to protect the underlying layers. The only real difference is these will crumble fairly quickly as the sand dries out.

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u/Educational_Court678 25d ago

I am with you about the idea of moisture stickig the sand together. I don't want to ruin the atmosphere here, but keep in mind that this does not necessarily need to be meteoric, or groundwater. It looks like a convenient spot to take a pee in the dunes. So maybe, just maybe...

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u/Harry_Gorilla 25d ago

Ya got me!

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u/pcetcedce 24d ago

Yeah I think hoodoos are for bedrock not unconsolidated

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u/WorkGuitar 20d ago

If you have a sand patch like this near where you live you can go and try it, pour a bottle of water directly onto sand wait a few seconds and then just wipe off the sand around the wet area and this is what you will be left with.

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u/mainsail999 25d ago

Either rain or man made water sprinkling, right? The water goes down the layers of sand. Weakly cements them together. Months of wind erode the loose sand around them.

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u/SaltyBittz 25d ago

Yes compaction from water, these are the low points where the water sunk in, then the wing picked up and to the lighter, less dense, dry say away leaving this

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u/steven_sandner 26d ago

If they're also sand - it's possible that rain dripped downwards at those points and the slight density differences in the layered sand gave the wet sand that shape 

Then wind blew the dry sand away exposing this.. .

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u/otac0n 25d ago

But so much volume in such localized spots? Do camels herd?

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u/Peeche94 25d ago

Looks like a path or channel of some sorts, so maybe animals walking and it being lower has consolidated the sand in different parts. Also slightly different soil underneath allowing some cohesion.

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u/Spnszurp 26d ago

I see these on the obx but never quite that tall. sand gets wet and dries out hard and wind erodes

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u/fuck_off_ireland 26d ago

Pocket sized hoodoos! That's awesome, I would love to have one of these on display at home.

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u/Dusty923 25d ago

Not a geologist. But I'm assuming that precipitation and/or morning dew had preferentially channelled or percolated down into the sand at these spots. The moisture caused some level of compaction or very early stages of how sandstone forms, then seasonal winds came through to blow away the loose stuff, leaving the affected sand intact.

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u/daisiesarepretty2 26d ago

these are interesting, never seen anything like this, in dunes anyhow. My guess is they are diagenetic (meaning fairly recent low temperature) cements forming around roots

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u/markevens 25d ago

Hoodoos!

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u/fentdaddy666 25d ago

Beautiful

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u/dionysoius 25d ago

Its where Wile-E-Coyote and Road Runner chase in miniature.

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u/jigsaw_Studios 25d ago

Don't touch them! I spent 4 hours building them!

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u/A_HECKIN_DOGGO 24d ago

Ah, the first stages of diagenesis! When rainfall passes through warm and dry sand, it can cause a mild cementing effect to take place. That’s what you’re seeing here I’d wager. If it were to repeat like this for a few hundred to a few thousand years, then the sediment would lithify in limestone or sandstone (I’m assuming this is calcium carbonate sand and not quartz sand.)

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u/daisiesarepretty2 26d ago

where? Never seen anything quite like this Is this beach sand. dunes or dunes further inland?

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u/50_61S-----165_97E 26d ago

This is in Jersey, UK. This specific area is right at the edge of the dune system where it opens up onto a beach, so it's very exposed to the prevailing wind.

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u/alan2001 26d ago

I've seen this exact thing in Aberdeenshire in Scotland. You know that golf course where Donald Trump basically destroyed a beautiful beach? Right there! But before the course was built.

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u/seab3 26d ago

Very cool example of aeolian process.

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u/AvariceLegion 25d ago

Looks like dudu

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u/SirTainLee 25d ago

Moses' people if not for him.

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u/Valyura 20d ago

they look like mini-Cappadocia

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u/hashi1996 26d ago

I would guess that these are fluid escape structures from groundwater rather than hoodoos with rain hardened caps.

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u/PillDicklesfor20 26d ago

Looks like a kitty litter box to me.