Saturday, July 17, 2010

The Great Sand Dunes, and friends

Wow, how long ago did I go to this place? I have been truly busy since I got back... I guess it must have been about three weeks ago. Wow. Well, here you are.


Great Sand Dunes National park, in south-central Colorado, is pretty fantastic. I would say it's worth a trip, but that's rather vague; for one thing, it's in the middle of nowhere, lots of nowhere, in which I felt quite close to falling asleep at the wheel and meeting my doom on a very long, straight road from nowhere to nowhere. But if you happen to be near the middle of nowhere already, it's definitely worth a visit.

It's not that large... the dunes look like, well, just some sand that made a little pile against the mountains. The tallest is maybe 700 feet. Looking at them is cool, but what I probably can't accurately convey here is just how cool it is to walk around on them. Before I try, some pictures:


The above looks like a cross between a black & white and a color shot, but it's just because the angle of light is so low on the dune in the foreground.


When I crested High Dune, which visitors all like to hike up to, I found this on the other side. Someone had saved me the trouble of writing my initials in the sand... if I'd wanted to.


Walking around in the dunes was fascinating to me as a geologist (which I am now!) because I could see, being formed in front of me, the types of structures I'd only seen before in rocks formed from ancient deserts.


The lines here, which cut each other off, mark the shifting direction of the dominant winds. Some of the sand is made of magnetite, which is both darker and heavier... wind and water "sort" sand into different sizes or weights, since, for instance, a wind of a given speed might be able to pick up quartz grains but not magnetite, so the two get separated. This separation allows us to see the lines above... I would say the lines are perpendicular to the dominant wind direction at the time they were deposited, but that would only hold for really straight-edged dunes. These dunes have wavy crests, which creates curved lines like you see above. It's a function of the amount of sand available and how much the wind shifts around.


The dunes look yellow in some pictures, but really they're brown. Sand is fascinating to look at up close. From the size, color, roundedness, and sorting (are they all one size, or many sizes?) of the grains, you can tell how far the sand has traveled and how long it's been sand. Quartz is very tough. If sand has been around a long enough time, it will be all quartz, all the other grains having broken down. This sand is only part quartz, and in fact, it was rock relatively recently.

I went for two walks on the dunes: one the evening I arrived, and one the next morning. In the evening, a good wind kicked up, which made things very interesting. I was wearing shorts, for one, and my calves were being absolutely sandblasted, which was not so much a wholly painful sensation as a very uncomfortable one. Maybe like having bandaids ripped off the entire surface of my calves, constantly. The sand also hissed, and rode over the surfaces of the dunes like mist. It was a full sensory experience.


It was like being on another planet, which I always love (which is why I go to these weird landscapes in the first place). Sunset was pretty:


...and it rained that night... in fact, it rained on and off throughout my visit, which made the dunes much easier to walk on. Also, except for the middle part of the day, it was rather cool there. The park is at about 8,000 feet, and I was all bundled up that night.

The next morning I went out for a walk on the north part of the dunes where nobody was. Soon I was out of sight of people, which was lovely, and the constantly changing curves and lines of the dunes all around me were really beautiful as I walked.


The bottom half of the above picture is the dune's slipface, or the back side, where the sand slides down after being pushed to the top by the wind. It's on the slipface that deposition of sand takes place; erosion takes place on the windward, or stoss side. So, in the picture above, the wind was most recently blowing toward us.


The dunes are host to several endemic insects, species found nowhere else on earth. This is not one of them.


This is my footprint. Every time I took a step, sand would avalanche downslope (in this case, to the right).


To create the circular shape in the foreground, sand was deposited on a curved surface, and later eroded into.


Medano creek is one of the "conveyor belts" of the park... it curves around one edge of the dunes, taking sand that blows off the edge of the dune field back to the beginning, where it's picked up again by the wind.


Here are my boots on a log with the Sangre de Cristo mountains in the background.


There was a forest fire burning in the park for a while before I got there... when I arrived it was only smoldering, up on a high mountain ridge in the distance. I had actually just walked out of the "closed" area when I took this picture; I hadn't seen any signs on my way in. Whoops.

I had a lot of fun at Sand Dunes... if you go, you must hike all around, and run down the dunes, et cetera. On my way back home I decided to stop at a park called Garden of the Gods, outside of Colorado Springs.

Colorado Springs has the worst traffic, ever.


But this is a deer. He was hanging out by the visitor's center.


Garden of the Gods is a small, crowded park, but it does have rocks standing up on end, which is nice. Superfically, these pinnacles resemble, say, those of Arches national park, but they were formed differently. At Arches, a flat-lying mass of sedimentary rock was cracked into vertical fins; here, the sedimentary rock was tilted until it stood upright. If it had dinosaur tracks, they'd appear to be walking up the pinnacles.


Garden of the Gods is probably worth a visit if you live in Colorado Springs. Otherwise, well. Just be satisfied with my pictures.


I took a picture of this sign because it illustrates the non-geological use of the word "formation" to mean, well, interesting rocks. This is different from the geologic use of the word, as I've probably mentioned in previous posts. Geologic formations have names, like the Morrison Formation. They are bodies of rock large and distinct enough to be useful for putting on maps. The rock in this picture is part of the Lyons Formation, which was deposited in an ancient desert. I would hate to think the entire Lyons Formation is unstable. Probably nobody should be building in the area Colorado Springs.

Well, perhaps soon I'll find time for a post about what all else I've been up to lately, which includes another trip to the landslide and activities with new friends around Denver.

2 comments:

Mom said...

Your photography skills never cease to amaze me!

Can't wait for your next entry.

Love,

Mom

Anonymous said...

I used to live there, in Manitou Springs. I would ride my bike through GOG every morning. It"s sad that Colo Springs has become so crowded,so paranoid, so Christian. It used to be a great place to live.