Activity discovered at Yellowstone Supervolcano – I talked about supervolcanos a while back. Don’t worry, it’s still in no danger of blowing up any time soon. (And here, we’re talking geologically soon, which is a much, much longer span of time than a human soon.) The two cool things in this article are the discovery that the Tetons are getting shorter, and that there’s a “bulge” that’s expanded and deflated at Yellowstone.
The Tetons getting short is interesting because, in the normal course of things, mountains do get shorter. That’s just the way things work. Mountains are built, erosion wears them down. However, the Tetons are getting shorter much, much faster than they ought to be. Now why is that? Mountain ranges are normally criss-crossed with faults, some of which may be very, very large. The faults are from where the rock broke, unable to handle the strain, when the mountain range was thrust up. There’s a very large, active fault at the feet of the Tetons. The way such faults normally work when active is that the valley at the foot of the mountains drops, while the mountains move higher up. Except that the fault between the Tetons and their valley is going in the exact opposite direction as normal – the valley is rising, the mountains are sinking. It’ll be interesting to find out what the exact mechanism is. The current hypothesis is that this abnormal movement is due to the expansion and contraction of the Yellowstone volcano; the volcano puffs up, it pushes on the valley. The valley creeps up the side of the mountains, which forces them down.
Now, the “bulge” is actually a pretty normal thing, volcano-wise. Contrary to what you might think, rock is actually very elastic. If put under pressure (pressure that isn’t overwhelming, that is) for a long period of time, rocks will deform. When rocks are put under too much pressure too fast, they will break, which is what causes faults. Volcanoes tend to bulge as magma builds up, putting pressure on them from the inside. (One of the heralds of the Mt. Saint Helens eruption was the enormous bulge on the side of the mountain.) In many volcanoes, this bulge builds up and builds up until the volcano erupts. In this case, the bulge deflated a bit before rising again, which indicates a temporary relief of pressure; it also happened pretty rapidly – at seven inches in three years, that thing is sprinting when you think about things geologically. The bulge is probably caused by the movement of magma from the mantel plume that feeds Yellowstone.
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Massive gypsum crystals in a cave in Mexico
These are SO COOL. Look at the first picture carefully – that’s a person in there for scale. These crystals are in a limestone cave, which was probably created by water from a hydrothermal vent coming in through a fault and dissolving the rock. (Limestone is very prone to dissolve when in contact with water.) The water deposited the minerals that formed these crystals (and the precious metal veins exploited in a nearby mine) and the crystals formed over time. The area is still very active as a hydrothermal vent; the temperature of the cave is around 125-150F and the air’s at a constant 100% humidity. Brutal!
If you didn’t know, hydrothermal activity is associated with volcanic activity. When rock is subducted at a plate boundary, it normally carries a lot of water with it. The water is superheated and seperates from the rock; it escapes rapidly through whatever avenues are available to it, normally through faults that form vents. Due to the nature of how the rock melts, the superheated water often carries rare elements with it (such as precious metals) that it deposits along the vents as it cools, moving to the surface.
The giant crystals in this picture are gypsum. Gypsum is a pretty cool mineral. It’s a 2 on Moh’s hardness scale, which means that you can scratch it with your fingernail. When you get a nice crystal that hasn’t been banged up (and it’s hard to find those, sometimes, because just about anything will mark gypsum because it’s so soft) they’re usually transparent. When you touch gypsum, it’s smooth and feels faintly soapy or waxy.