Geological Oddities Part 1: Columns, Crystals, and Concretions

Geological oddities are a lot of fun, but this new series isn't solely about having fun with them- it's also about putting them in geological context, and exploring what these variations from the norm have to say about our planet. Also, though, it's definitely about having fun with them. And about having way too many blog post series going at once.

In 1941, California constructed the Long Valley Dam, resulting in the birth of Crowley Lake. While it was originally meant just as a reservoir for Los Angeles, that ever-thirsty environmental catastrophe, it's since become a major tourist destination, especially for trout fishing. Something curious occurred shortly after the birth of Crowley Lake, however. The powerful waves on the lake began to erode away inexplicable rock columns on the eastern shore of the lake.
There are nearly 5,000 of these cylindrical pillars today, coming in a variety of sizes. It wasn't until 2015 that researchers figured out the geology behind the columns, however.

Skip to 1:06 for a closeup on the columns. [Video source]

Three quarters of a million years ago, a supervolcano erupted with a blast 2,000 times bigger than the 1980 Mt. St. Helens eruption, forming the massive Long Valley Caldera and coating much of the American West with hot volcanic ash. The Bishop Tuff, the volcanic rock that formed from this ash, is in places thousands of feet thick. (Tuff is welded volcanic ash. It has a wide range of material strengths depending on its formation conditions, so jokes and puns about its toughness are common.) It would have taken a considerable time to cool, and sometime during that period- likely fairly early on- snowmelt began seeping down into the ash. As volcanic ash (and other volcanic features) cools from the top down, the water began boiling as it went farther and farther down. This generated evenly spaced structures akin to heat pipes. Erosion-resistant minerals were deposited in tiny spaces within these convection pipes, making them more erosion resistant than the surrounding rocks.

The Crowley Lake columns aren't completely unique- similar formations exist in Mexico and New Mexico. Still, they're extremely unusual formations, and definitely deserve the label of oddity. Geologists were fairly easily able to figure out how they were formed when they really started looking into them- a trend which holds true with a great many of the geological oddities around the world. Frankly, some of the greatest geological mysteries rest within really boring looking rocks, while many of the strangest have proved quite easy to figure out. That's not always true, but it does somewhat bring up questions about how we should be thinking about geological oddities.

The Cave of the Crystals in Mexico. [Image source]

The Cave of the Crystals is one of the best known geological oddities on Earth. There have been more than a few posts about them here on Steemit, even. Some of the selenite crystals in the ~1000 ft deep cave approach 40 feet in length. They're formed thanks to lying atop an ancient fault leading into a magma chamber ~3-5 km (2-3 mi) below the cave. The magma heats the groundwater, saturated with sulfide ions, and due to the constant heating it allowed the crystals to grow over half a million years- and the longer crystals have to grow, the bigger they can get. Slower is better for crystal formation. It's still extremely hot in the cave- to the point where scientists need to wear special refrigerated suits when accessing the cave from the mine it's connected to- so there is still crystal formation going on.(In fact, as the mine is no longer operating there, the pumps have been shut down and the cave re-flooded.) So, again, fairly easily comprehensible, if unusual, formation conditions for the cave.

So many geological oddities are the product of normal geological processes- but often somewhat exaggerated or fringe conditions for said processes. Geological features are merely the leftover products of geological processes, so it's quite productive to think about them on a bell curve, with the most common morphologies for geological features near the center, and more unusual ones as outliers. They can be the result of two processes mixing that don't often mix, or the result of processes as they weaken and sputter out, or the result of plain old weird luck.

The huge sandstone concretions of the Red Rock Coulee. Apologies for the small image size, it was the only image of them labeled for reuse I could find. [Image source]

Formation, however, isn't the only important set of processes to watch for in understanding geological oddities. When geological features are deposited, they don't just remain as mere geological memories of the past- they continue to be acted on by other geological forces, not least of which is erosion. Many geological oddities formed in utterly normal manners, and were only rendered oddities by later circumstances. The Red Rock Coulee in Alberta, Canada is a great example. This rugged prarie is covered in massive, semi-spherical red boulders, some measuring as much as 2.5 meters across. There are no nearby cliffs or other visible means of them getting there- and, in fact, they weren't transported there, but actually started there.

The relatively thin soil in the region results in heavy bedrock erosion. As the sandstone bedrock is eroded away, it leaves behind the boulders, which are actually concretions. These sandstone concretions formed when layers of sand, calcite, and iron oxide formed around a nucleus of shells or other detritus on the seafloor. This is an extremely common process, and concretions can be found in marine sandstones (especially those formed in relatively shallower depths) all over the world- there are tons of them along the Oregon coast, for instance. Concretions are significantly more erosion resistant than regular sandstone, so it's not unusual for them to be left behind after erosion occurs. The unusually large size of these concretions, however, means they accumulate in much larger than usual numbers and prominence in Red Rock Coulee, and remain more resistant to weathering and transport for longer.

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