Caving in Montana: Crystals Galore

These are well-known caves that are publically accessible with a permit. If you would like more information, or would like to view any of my site-specific references, please feel free to send me an email at helena.heliotrope at gmail.com. If you’d like to visit the caves, please contact the BLM Field Office in Cody at 307-578-5900, and ask about their caves!
In the fall of 2009, I got to go on an epic caving weekend near the Montana-Wyoming border. I talked briefly about some interesting chert nodules here, but I was honestly holding out on the best stuff: the formations.
The caves here are formed in the limestones and dolomites of the Madison group. These rocks formed between 360 to 325 million years ago, in the Mississippian, when a relatively tranquil, shallow sea covered the area. Like most seas, this one was filled with small organisms that had calcium shells or skeletons (such as corals or amoeboids.) When these organisms died, their decaying corpses were slowly compressed into limestone. Above the limestone lies a layer of reddish sandstone called the Amsden laid down in the Pennsylvanian, visible as the red streak in the above picture. After undergoing a sequence of uplift and subsidence, it was uplifted to its current level during the Laramide orogeny, about 70 million years ago. This created joints in the limestone that would someday become caves.
(It’s a really structurally interesting area – some of the nearby mountains are uplifted in a giant anticline, while the ones in the above picture are fault blocks that were tilted upwards.)
The Madison group stretches from South Dakota to eastern Idaho, and from Canada down into Colorado and Arizona, although the name differs regionally. Since limestone is very soluble, it’s chock-a-block with caves, including Lewis and Clark Caverns in Montana. Because of its solubility, it forms a very important aquifer, and has produced a prodigious amount of oil – over 1,400,000,000 barrels. (Pretty impressive for a bunch of dead sea critters!)These caves were eroded as the basin lay beneath the water table, in a process called phreatic erosion. Phreatic erosion occurs as the water flows through cracks and joints, eroding passages through the limestone. This passageways travel in all directions: the above photo shows a vertical, cream colored passage cutting through different bedding planes. Additionally, we saw some collapse along bedding planes, which created some fantastic flat roofs, visible here in the greyish section. Dating caves can be difficult (much like men), however some ash found in these caves is from an Yellowstone eruption 640 thousand years ago.
(I apologize for the poor picture – it’s quite difficult to take decent photos of large cave rooms without secondary light sources.)
This is a trace fossil we found on one of the bedding plane ceilings – it’s where a sea creature was burrowing, or eating, or squirming along. (The paleontologist on the trip provided some more details, but I’ve unfortunately forgotten.) I had never seen a fossil in the wild before, so this was one of the trip’s highlights.
The first cave we went to is the most challenging cave I’ve been in so far, despite being entirely horizontal. The entrance is through a 100’ long crawlway – which sometimes is only 15” tall. (I definitely got stuck a couple times!) The floor of this crawlway is thickly coated with radon-laden dust: to avoid developing radioactive cavers, the BLM limits the time you can spend in the cave each year. We wore dust masks, to cut down on the amount of junk we inhaled, but that only served to make me more claustrophobic.  This was even more heightened by the heat – it was the warmest cave I’ve ever been in. It was a pretty rough beginning, but we were richly rewarded for all that effort with masses and masses of my favorite formation – helictites.
I didn’t have my camera that day, but I did the next day, when we visited the second cave. The day of this trip, snow was predicted, so we only spent the morning underground. (The road to the caves requires a 4wd vehicle generally, but is reportedly impassable in bad weather.) Luckily, as we ascended out of the cave right as the snow began falling, and made it to paved roads just in time.
The caves have a wide variety of calcite formations, including helictites, rafts, and some really large cave popcorn. Additionally, they have gypsum flowers and crusts, epsomite crystal curls, and aragonite needles. These all form near each other, making for some truly impressive photographs.
This last photograph is an interesting chunk of yellow and red crystal crust that was forming in a hole in the ground. I still don’t know what it is…
This is the underside of a rock, absolutely encrusted with black crystals.
As we headed back to civilization, there was an antelope hanging out, clueless about what lay beneath its small cloven hoofs.

Amurrica

This is a map I made for my first GIS class, in 2009. The goal was to subdivide the country into regions, not in accordance to state lines.

My aim was to be sassy, but not wholly offensive.

I should really use my powers for good...
 

(I’m not sure why it’s stretched – I think the projection is incorrect.)

Claymation, Bicycles, Velociraptors, and my Sister

This is the video I made for my sister’s cancer charity! The creation of this really was a family effort, involving both my parents, myself, and two of my uncles. Watching the claymation mitosis come together from 175 individual images was incredible. When I was younger, I attended a summer film camp for girls, and it was nice to see that I hadn’t lost all the skills I learned there. It took a looong time to get up to speed on the new editing software, sort through all the clips, and polish it into a finished product, but I’m really quite pleased with the final results.

Even if you can’t afford or don’t wish to donate to her cause, you should follow her twitter or tumblr, because she’s going to be posting exciting things as she travel across the country!

Plus, she’s probably going to cure cancer someday, so you might want to just learn her name now. When they finally name element 118, it’ll be “Rosemarium.”

AW #30: The Moon is Made of Toasted Coconut.

The Accretionary Wedge #30 was a Geologic Bake Sale! Baking is one of my favorite hobbies, and I wanted to do something new and exciting for this challenge.

When I saw this recipe, inspiration struck. The flakes of coconut lay so lightly atop one another, as though they were gently supporting each other without actually touching…

… which is exactly what happens on the moon!

Regolith is akin to soil on the Earth: it’s the layer of unconsolidated material over the bedrock. The moon’s regolith is composed of  bedrock pulverized by meteorites and “micrometeorites” – meteorites that are under a millimeter in size. Over the long life-span of the Moon, these micrometeorites have succeeded in completely altering its surface. (Just goes to show how concentrated effort over time can yield immense results!)

The top portion (3 – 5 m) of the regolith is composed of really fine-grained, loose particles. These sort of “float” on the surface: they are held together in layers by Van der Waal forces. (Van der Waal forces occur when charged molecules are very gently pulled toward oppositely charged molecules, and are very weak.) This is very similar to the uppermost, lightly held together layer of coconut.

The bottom portion of the regolith is more solid, and frequently referred to as the “megaregolith.” This is a layer of very fractured bedrock, 2 – 3 km thick on the highlands, and about 1 km thick on the maria. Here, it’s the more consolidated layer of coconut.

Much as Earth-soil has different varieties, the regolith has two different components: glass spherules and agglutinates. Glass spherules form when melted rock from a meteor impact solidifies in mid-flight, not having enough time to form a crystal structure. (Similar to how obsidian is formed very quickly from lava.) Agglutinates are glassy breccias composed of rock bits and vesicles containing gas from solar winds, all held together with rapidly melted rock.

Under all of that is the bedrock of the moon, anorthosite and basalt. I decided to have a simple basalt/brownie bedrock – this section of the moon is somewhere in a flood-basalt mare (or "sea”,) to account for it’s thin layer of megaregolith.

 

These are the ingredients needed to create an edible Moonscape. Some of these were doubled, as I needed to make some extra bedrock, which I flavored with two packets of that Starbucks Via instant coffee. Additionally, I used 10 oz of coconut, and an extra splash of milk, to increase the bulk of my regolith.

And this is the Moon, post-baking! Note how that regolith seems soft and fluffy.

This is a futuristic moon bubble, to protect this patch of regolith from any wandering spacemen…

… of which there were several, repeatedly! Colonizing in Moon lava tubes might be a better idea after all…

 

After everything had a chance to cool, I set about to make the crater. (We’ll discuss actual crater formation in a minute!)

To do this, I punched a hole in the coconut slab, and set it atop the brownie bedrock layer. There was some minor excavation of that layer as well. Using bits of brownie, I constructed the central peak of the crater, and placed some fragmented bedrock inside the crater. Using the extra coconut slab, I carefully compiled a reverse layer of ejecta around the crater.

To prepare the melt for the inside of the crater, I melted a Cookies and Crème bar in the microwave (not for too long or it burns!) and poured it into the crater. After engaging in a little careful destruction to create collapsed crater walls, the Moonscape was done!

Here’s a close up of the side, giving a better look at the overturned regolith/ejecta layer, and the added bedrock.

(A simple line diagram of central peak craters is found here, in case the deliciousness of mine is distracting.)

When a meteorite impacts the moon, the ground is rapidly compressed downwards, away from the incoming meteorite. After the  meteorite impacts, this pressure is released, allowing the material to rapidly – and explosively – decompress, creating the crater.

When the crater floor decompresses, the bedrock under the crater rises up to create a central peak – if the crater is larger than about 50 km. (Craters larger than a couple hundred km in diameter are called impact basins, and develop both a central peak and 1+ upraised rings inside the basic. Craters smaller than 50 km are called simple craters, and lack the central peak entirely.)

When the compressed regolith rapidly expands, it blows the surrounding regolith away from the crater, creating a ring of over-turned stratigraphy. Because of this phenomenon, the older and deeper material gets thrown farthest from the center of the crater. This is visible in the layer of brownie bedrock atop the ejected coconut.

Frequently, the bedrock in the crater floor is fractured, and magma seeps through to the surface, creating a puddle of magma-cemented breccia, sometimes referred to as “melt” – or, in this case, the melted chocolate. Additionally, the walls of medium and large craters frequently suffer from landslides, due to their tall, steep walls.

 

Now, there are two scientific inaccuracies in this edible diagram: 1) there should be a larger cloud of finer ejecta, and 2) for the bedrock to be so exposed, the crater should be larger in diameter.

But, space constraints aside, it was a fairly accurate model, and tasty to boot!

(My main references for this were my notes from a planetary geology class I took a couple summers ago. Since those aren't online, I've merely linked to some informative wikipedia pages. Say what you will about wikipedia's accuracy, it's still a good starting point!)

Montana, Chert, and the 1960s.

Two years ago, this rock really caught my eye while I was caving in the Madison Group of Montana.
First of all, there’s a nifty calcite or gypsum encrusted pocket, which looks much like a sparkly pothole…

(My assumption is that this formed as water seeped through the limestone into a small hole, and then crystallized on the hole’s walls.)
Then there’s the missing chunk, which gives a nice look at a crazy banded chert nodule.

If that chert nodule embodies John Lennon’s “Magical Mystery Tour” era, this nearby chert nodule is more Jackie Kennedy:

Way to keep it classy, chert.