The other reason for visiting Yellowstone is to view the astonishing geographic/geologic features. Although Old Faithful is the very icon of Yellowstone, it represents only one aspect of the park. Yellowstone sits atop an ancient caldera, one which has blown up catastrophically about every 640,000 years, the last time being about 640,00 years ago. For comparison, the Lava Creek supereruption about 1.2 million years ago produced about 2500 times as much ash as Mt. Saint Helens. Herds of animals in Nebraska were killed in the resultant ash fall, as seen at Ashfall Fossil Beds State Historical Park. The Yellowstone caldera is situated over a hot spot in the earth's crust, similar to Hawaii, where molten magma is unusually close to the surface. Like the Hawaii hot spot, it is showing apparent motion, though what is really happening is that the overlying tectonic plates are sliding over a stationary hot spot. The Yellowstone hot spot is apparently moving to the east-northeast. Maybe it will eventually warm up upstate New York, though my limited experiences with that region make me doubt that a single supervolcano will have the necessary heat.
As a result of the continuing hot spot, Yellowstone has geothermal features
virtually throughout the park. Over half of all the world's geysers are found here, and other thermal features include fumaroles, hot springs, and steam vents.
The other geologic/geographic features are usually related to this underlying volcanic history. The "average" elevation of Yellowstone's main features is about 7300' (which makes the boiling point of water about 199 degrees, an important fact for understanding some of the thermal features). The average elevation is about 8000', but ranges from 5282' to 11,358 at Eagle Peak. That fact, plus the variation in geographic features such as canyons, mountains, streams of various sizes, and thermal features makes for a very diverse environment, with multiple micro-climates.
Although Eagle Peak goes up to 11,358, Yellowstone is more about canyons, lakes, rivers, and thermal features than mountains. Yellowstone is the headwaters of the Yellowstone River, which is the longest undammed river in the lower 48 states, eventually emptying into the Missouri River and thence to the MIssissippi and then the Gulf of Mexico. Its grand canyon, with yellow walls coming from thermally altered rhyolite rock, gives the name to the river, the park, and the region.
Lake Yellowstone, centered over the caldera, is the largest
high-altitude lake in North America. Both the Mary Bay and West Thumb are the result of gigantic hydrothermal explosions, and there are hot springs underneath the lake. At Mary Bay, the hottest temperatures in the park are recorded. But the lake itself is cold, the recipient of runoff from the snowfields and glaciers. It, and the Yellowstone River, house the world's only population of cutthroat trout, which are threatened by the much larger and artificially introduced lake trout. The park service now has a program of gill-netting for the lake trout which catches thousands of them yearly.
The ancient caldera rim measures about 35 by 45 miles, but is now only visible in certain spots, such as where Gibbon Falls goes over the old rim. For most of its circumference, it has been covered by subsequent lava flows, ash eruptions, and other geologic happenings, but it is clearly visible from space and the air.
Perhaps the most viewed and photographed feature in the park, other than the geothermal features such as Old Faithful, is the Grand Canyon of the Yellowstone and the associated Upper Falls and Lower Falls. You are able to hike down to the brink of
each of the falls, where you stand on a platform just a few feet above the rushing water. In a year like this when there was much more snowfall than is usual, the rush of the water is overpowering. The views from Artists Point and Inspiration Point have been photographed by the best, and painted by such luminaries as Thomas Moran and Albert Bierstadt.
The ash eruptions also repeatedly covered local forests with ash, immediately entombing them and allowing for petrification of the wood, giving Yellowstone one of the largest petrified wood stands in the world.
One final feature to mention is Isa Lake. It sits directly on the Continental divide. By some conjuring of geography, water that flows in from the west ends up flowing east to the Gulf of Mexico, while water flowing in from the east ends up flowing eventually to the Pacific.
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