The great sand dunes in the sky

Craig Brokensha
Swellnet Analysis

While chasing snow on a recent holiday in Colorado I came across one of the most radical landscapes I've seen.

It wasn't an abrupt mountain face but a Mars-like landscape of sand dunes in a remote and desolate corner of the otherwise snow-bound state.

The dunes are over 200m high and sit 2,650m above sea level, higher than Australia's largest 'peak' and have an appearance not dissimilar to Stockton Bight.

The dune field spreads out for miles, a geological wonder tucked into the base of the Sangre de Cristo Mountain Range immediately to the east which contains a handful of Colorado's '14ers'. That being mountain peaks surpassing 14,000 ft (4,267m), which in Colorado number 53.

The first thing I thought was, How did the sand dunes get here? They're over 1,000km from the nearest ocean and far above sea level.

Recent studies have identified the source of the sand and its age by looking at the surrounding geography and geology.

The sand dunes sit in the north-east corner of the San Luis Basin, a diamond-shaped basin that's bound to the north by the junction of the Sangre de Cristo Mountain Range and San Juan Mountains, while to the south the Sangre de Cristo Range meets the Tusus Mountains.

During glacial times the Rio Grande River, which runs down from the San Juan Mountains into the western side of the basin, delivered large volumes of meltwater and sediment, flooding it and forming Lake Alamosa which consumed the northern half of the basin.

A large alluvial fan also formed at the base of the Rio Grande and when Lake Alamosa drained rapidly some 440,000 years ago due to its volume and pressure purging volcanic deposits at its southern end, this provided the sediment for which the sand dunes could form.

Predominant west to south-west winds blew the sand east over hundreds of thousands of years until it was captured in the corner of the Sangre de Cristo Mountain Range. This and the swing in local winds from west to east during storm periods results in the formation of reverse sand dunes which remain fairly stationary and grow in height instead of moving across the landscape.

Analysis of diverted rivers flowing down from the Sangre de Cristo Range identified that the earliest the sand dunes could possibly have formed was 130,000 years ago, but sometime after the lake drained 440,000 years ago.

Further analysis of the sand dune profile identifies that only 11% of the material is from the local Sangre de Cristo Mountains immediately to the east, with the majority of the sediment originating from the San Juan Mountains some 80km to the west.

All this geology talk may only interest some, but for anyone travelling to Colorado I highly recommend heading to and camping in the Great Sand Dunes national park to enjoy the juxtaposition between the dunes and towering snow-covered mountains.

Comments

walter-r-white's picture
walter-r-white's picture
walter-r-white commented Friday, 5 Apr 2019 at 9:37am

Interesting maths there. 14,000ft mountains start at 14,000ft, otherwise known as 4267m not 2470m. Assuming that's just a typo :-)

Don't take me too seriously.

Craig's picture
Craig's picture
Craig commented Friday, 5 Apr 2019 at 9:40am

Ah, yes, picked that one out nicely. Fixed. And cheers.

walter-r-white's picture
walter-r-white's picture
walter-r-white commented Friday, 5 Apr 2019 at 9:39am

Interesting article btw

Don't take me too seriously.

zenagain's picture
zenagain's picture
zenagain commented Friday, 5 Apr 2019 at 9:53am

Fascinating stuff, could only imagine how fragile this place would be.

Hows the air up there? I'm not sure but i believe breathing gets more laboured over about 3000m?

More importantly- snow quality. Get some faceys?

Watashi wa metabo oyagi desu.

Craig's picture
Craig's picture
Craig commented Friday, 5 Apr 2019 at 10:14am

I didn't really struggle breathing or working up that high Zen, but I did get a bout of altitude sickness on our first day out. A migraine like headache and nausea before vomiting on the way home, but after sleeping it off I was good some 6-12 hours later and found no further ill affects.

Face shots.. indeed..

zenagain's picture
zenagain's picture
zenagain commented Friday, 5 Apr 2019 at 10:53am

Throwing ice-buckets.

Yew!

Watashi wa metabo oyagi desu.

Chris Buykx's picture
Chris Buykx's picture
Chris Buykx commented Friday, 5 Apr 2019 at 10:22am

Yeew - more geology on Swellnet please!

hillsintas's picture
hillsintas's picture
hillsintas commented Friday, 5 Apr 2019 at 11:08am

2nd that motion.
I have had dreams of waves breaking in places that they should not be breaking.
maybe they did in the past?

Tenn's picture
Tenn's picture
Tenn commented Friday, 5 Apr 2019 at 11:04am

Wow what an unreal landscape ! Must have been an amazing journey giving me the travel bug

Sprout's picture
Sprout's picture
Sprout commented Friday, 5 Apr 2019 at 11:24am

The work of Graham Hancock and Randall Carlson is worth a read regarding geology. Hancock goes on to make some 'interesting' assumptions, but even if they're not to your taste, the facts they put forward are really interesting and are continually being backed up by new discoveries made each year.

hillsintas's picture
hillsintas's picture
hillsintas commented Friday, 5 Apr 2019 at 12:00pm

An interesting author.
Earth in Upheaval
by Immanuel Velikovsky

Earth in Upheaval (1956) is Velikovsky‘s third book, which he describes as:

“… a book about the great tribulations to which the planet on which we travel was subjected in pre-historical and historical times.
The pages of this book are transcripts of the testimony of mute witnesses, the rocks, in the court of celestial traffic.
They testify by their own appearance and by the encased contents of dead bodies, fossilized skeletons.
Myriads upon myriads of living creatures came to life on this ball of rock suspended in nothing and returned to dust. Many died a natural death, many were killed in wars between races and species, and many were entombed alive during great paroxysms of nature in which land and sea contested in destruction.
Whole tribes of fish that had filled the oceans suddenly ceased to exist; of entire species and even genera of land animals not a single survivor was left. ..”
“I had intended, after piecing together the history of these earlier global upheavals, to present geological and paleontological material to support the testimony of man.

kevinborrich's picture
kevinborrich's picture
kevinborrich commented Friday, 5 Apr 2019 at 1:20pm

In springtime with snowmelt that joint produces a standing wave. Saw it in action a few years back. One of the most interesting landscapes Ive seen.
https://www.youtube.com/watch?v=q2uSiOfGcRc

crg's picture
crg's picture
crg commented Friday, 5 Apr 2019 at 1:40pm

Cool article...thanks Craig.

I'm not cheap,
But I'm free.

velocityjohnno's picture
velocityjohnno's picture
velocityjohnno commented Friday, 5 Apr 2019 at 2:02pm

Very interesting and such a juxtaposition!
I'll bet you'll take a sand board next time Craig. Sandboarding used to be our cross training for the snow when in WA. Climbing back up the dunes got you fit!

Craig's picture
Craig's picture
Craig commented Friday, 5 Apr 2019 at 2:06pm

We actually ran into some ladies on top the dunes that night watching the sunset and they had snowboards and skis! Haha, had a good run down the Star Dune though not sure how many of those the board would stand up to.

velocityjohnno's picture
velocityjohnno's picture
velocityjohnno commented Friday, 5 Apr 2019 at 2:16pm

Wow, they were using proper snow gear and doing OK? We found the thicker wooden sand board was a bit better, with a floating edge of about 5mm thick and copious candle wax. You can *kind of* mimic turns and traverses and little jumps are fun.

Subsequently the dunes were over-run by 4wheel motorbikes etc and it's a bit more boganised these days. I can remember my littlest standing at the top of a crest, then riding down having a ball, then a bloody troopie appeared from the other side right where he was just standing!

Speaking geological, this year I'm headed back to those places and have mind to take a day and go looking for those 'chevrons' (mentioned in Swellnet's satellite finding biggest wave thread) from around there, supposedly caused by said monster wave some thousands of years ago. (There's nice sand dunes there too!) Now what does a chevron look like again??

Craig's picture
Craig's picture
Craig commented Friday, 5 Apr 2019 at 2:19pm

Yeah it took half the slope to get the speed to do a turn, and the ladies not so much just straight lining it. Although the skier got lots of little hops in.

Ah bummer re the dunes now.

Vic Local's picture
Vic Local's picture
Vic Local commented Friday, 5 Apr 2019 at 2:25pm

Does this article mean you can tax deduct flights to and from, and accommodation in, Colorado?

"angry online, smiley in the brine"

Craig's picture
Craig's picture
Craig commented Friday, 5 Apr 2019 at 2:26pm

I think that would be pushing it for this.

memlasurf's picture
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memlasurf commented Friday, 5 Apr 2019 at 3:00pm

Snow looks unbelievable although I don't know much about skiing (too fricken expensive here). That is a great quirk of nature and it looks like none of the vegetation has adapted to colonising it, even after all those years. I suppose the surrounding ecosystem is not set up for this anomaly. What always gets to me is how alien the landscape in the USA is. So dramatic on the western side and so bleak in winter on the east. Interesting and worth a look but I get homesick for the Euc woodlands, heaths and schlerophyll forests in my part of Oz whenever I get into a landscape such as this. Home is where the heart is.

Bnkref's picture
Bnkref's picture
Bnkref commented Saturday, 6 Apr 2019 at 7:30am

Hey Craig how come there’s no snow on the sand? Seems high enough. Is it a shadowing effect from the mountains?

Craig's picture
Craig's picture
Craig commented Saturday, 6 Apr 2019 at 1:23pm

There was but it melted probably the day before we got there. Still some on the tops of the dunes and moist under the dry top sand. Also it feels like it's in a bit of rain shadow on the eastern side. The San Juan mountains get some of the most snow in Colorado and it's less so on the next Sangre de Cristo Range.

plops's picture
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plops commented Sunday, 7 Apr 2019 at 7:01am

There’s a very similar sand dune formation inside the Death Valley national park, it was near the stove pipe wells campgrounds. Gotta love the western states if your a fan of mountains and geography!