I have said time and again that this past summer was stimulating and educational for us, but I know as a blogger that my passions may not match yours so if geology isn’t your thing, feel free to look at the pretty pictures instead. I say this as someone who gave geology a mere passing nod until I supported a couple of naturalist courses on the subject. Now I am spellbound and will never look at Yellowstone the same, nor anywhere else for that matter, where geologic forces come together to create majestic peaks, valleys, and canyons.
I can’t say which of the Yellowstone Forever field seminars I supported was my favorite, but without a doubt I can say that the instructor who led the Thermal Biology and Geology course this summer, Joshua Theurer, is extremely bright, passionate about Yellowstone, and can hold a student’s attention like the most seasoned of instructors. I was fully engaged in both his field seminars I supported and look forward to participating in more of his classes in the future.
Joshua’s “Observing Thermal Geology and Biology” course, which followed on the heels of Virginia’s “Landscape Geology” class (also wonderful), was fortuitous for me (or so I thought), giving me a leg-up, as it were…hardly. This is a complex subject, and we were required to complete an exercise before the end of the course, in order to receive credit for this naturalist class. I could go on and on about everything I learned but instead will touch on some of the highlights, so as not to put anyone to sleep.
Imagine, if you will, the earth as an egg:
- The outer layer of the earth, the crust, is analogous to the shell of the egg. It is ~ 25 miles thick. Yellowstone has a much thinner crust than average, as little as three miles thick in places.
- The mantle, which makes up the bulk of the earth and moves in enormous convection cells, is like the egg white. It averages about 3000 miles in thickness.
- The core of the earth, resembling the egg yolk, is composed mostly of metals and acts as a nuclear reactor, our primary heat source.
There are about two dozen hot spots on earth, with Yellowstone being one of the largest. The theory is that a hot spot originates at the core of the earth and doesn’t move. The continental plates move across them.
Given the 10,000+ hydrothermal features in Yellowstone, one would assume a significant magma chamber below the park, deep in the mantle of the earth, and you would be right. In 2011 the University of Utah’s research concluded that this chamber was at least 400 miles thick and this was all they could determine as their equipment went no further. In 2015 they discovered a “mantle plume” of roughly 1000 miles below the original magma chamber, a reservoir 4.5 times larger than their initial discovery! We now believe there is enough magma below Yellowstone to fill the Grand Canyon 11 times. Although this sounds ominous, given Yellowstone is classified as a “supervolcano”, scientists don’t expect a major eruption is in the park’s near future, and feel that there would be weeks, if not months, of increased seismic activity prior to such an eruption.
Day one our course took us to one to the hottest and most rapidly changing thermal areas in all of Yellowstone – Norris Geyser Basin. Mechanically it functions like other geyser basins but is far more complex, due to the converging of three fault lines beneath it.
Porcelain Basin resides within Norris and was so named for the milky color of the mineral deposits found here.
There are four types of thermal features found within the park:
- Hot springs – most common and have no constrictions. Water continually circulates, preventing the water from reaching a temperature needed to produce an eruption. The deeper the blue color, the hotter the water. Deep blue signifies temps of at least 159º F.
- Geyser – around 500 in the park. These features erupt when the gas bubbles’ surface area is so great that the water is lifted outside the reservoir.
- Mudpot – most acidic, with a pH of 2 or less and a limited water supply. Gases convert rock to clay.
- Fumarole – known as a steam vent, and is the hottest hydrothermal feature in the park. Water is converted to steam even before it reaches the surface, and is usually announced with a loud hissing sound. Temperatures can reach to 280º F. Norris’ hillsides are dotted with these steam vents.
Hot springs, geysers, and fumaroles can be found within the Norris Geyser Basin. I am not aware of any mudpots within Norris, but some can be found just a few miles south at Artists’ Paintpots. The varying colors found within these thermal features are due to special microbes, called thermophiles, that make their home here, and the off-putting smell (think rotten eggs) is due to the elevated levels of sulfuric acid and hydrogen sulfide gas found in the thermal features.
And one of my favorites…
Disclaimer: The views expressed here are my own and do not necessarily represent the views of Yellowstone Forever.
Next Up: Day 2 of Thermal Biology, where travertine abounds.
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