Yellowstone National Park
We are around 400 miles as the crow flies from on of the great natural wonders of the world. The geology that our first national park exhibits on the surface far outshines any scenic beauty that of course is very impressive as well. Even a child can tell upon a short visit, that Yellowstone is not your typical back yard.
I mentioned in a previous column that Yellowstone has the worlds largest volcano in it’s boundaries. This kind off volcano is called a Megavolcano and in this case the crater is about 70 miles across. The crater is a type called a caldera. When molten magma from deep in the earth pools close to the surface, it causes the ground to swell like a pimple. If that swell gets a crack in it that releases the pressure look out. All the dissolved gases in the molten rock tries to escape (like shaking a closed pop bottle then opening the lid!) and you have a really big bang. The fizz turns out to be pulverized rock powder (ash) and with a volcano that big there is a lot of it.
Yellowstone is volcanically active but fortunately is not currently erupting. The previous three caldera eruptions occurred a 1.8 million years ago (MYA), 1.2 MYA and .6 MYA (Do you notice the pattern here?) You could extrapolate that the next one is due anytime. You might be right but don’t hold your breath. If Yellowstone did blow it’s top, the event would be world changing in it’s scope. The falling ash footprint would cover most of North America with any where from hundreds of feet to inches of the heavy stuff. Powder River County having a front row seat to the falling molten glass fountain that would be splashing on the Big Horn Mountains. Any life within a 500 mile radius would be hard pressed to survive. This kind of event would make the 1979 Mt. St. Helen’s explosion look like a hiccup.
This volcanic activity of course is what gives Yellowstone all the really cool hydro-thermal stuff like geysers, hot pots, steam vents and other attractions. One of the negative things that is highly likely to occur is a big earthquake. If you think as the bulging molten rock under the ground of Yellowstone like a speed bump that the North American continent has to ride up and over as it slowly drifts to the southwest, you will notice the surface expression of the stress field generated. Look at any topographic map of the western US and you will see that mountain ranges occur west toward Chalis Idaho and south to Salt Lake City from Yellowstone in ranges lined up like ranks of so many soldiers. These ranges are literally ripples of the “bow wave” of the Magma Chamber under Yellowstone. All of these ranges are under huge seismic stresses induced by the shearing stress resultant from these conditions. The largest modern scientifically measured earthquake in the Lower 48 was the 1959 magnitude 7.5 quake just 50 miles west of Yellowstone Park. The next biggest event was the 1983 magnitude 7.3 quake near Chalis Idaho. Both of these quakes were directly related to the the seismic stress field generated by Yellowstone. Several variously sized population centers like Salt Lake City Utah, Jackson Hole Wyoming, Afton Wyoming, Kemmerer Wyoming and West Yellowstone Mt lie directly on mountain ranges stressed by this phenomena. Earthquake insurance, strict application of seismic building codes and not building under a large boulder strewn steep hillside seems to be a good idea there.
It is good to know about how your neighbors live.