Geology
Firehole River near Excelsior Geyser.
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Yellowstone is at the northeast tip of a smooth U-shaped curve through the mountains, which is now the Snake River Plain. This curved plain was created as the North American continent drifted across a stationary volcanic hot spot beneath the Earth's crust. This hot spot used to be near what is now Boise, Idaho, but North America has drifted at a rate of 4.5 centimetres a year in a south western direction, shifting the hot spot to its present location.
Yellowstone Caldera is the largest volcanic system in North America. It has been termed a "supervolcano" because it was formed by exceptionally large explosive eruptions that formed the caldera. This caldera was created by a cataclysmic eruption that occurred 630,000 years ago that released 1000 cubic kilometres of ash, rock and pyroclastic materials (this is 800 times larger than Mount St. Helens' 1980 eruption) and formed a crater nearly a kilometre deep and 45 by 25 miles in size (the size of the caldera has been modified a bit since this time and has mostly been filled-in, however). The welded tuff geologic formation created by this eruption is called the Lava Creek Tuff. In addition to the last great eruptive cycle there has been two others in what is now the Yellowstone area.
Each eruption is in fact a part of an eruptive cycle that climaxes with the collapse of the roof of a partially-emptied magma chamber. This creates a crater, called a caldera, and releases vast amounts of volcanic material (usually through fissures that ring the caldera). The time between cataclysmic eruptions in the Yellowstone area has ranged from 600,000 to 900,000 years but the small number of such climax eruptions can not be used to make a prediction for the time range for the next climax eruption.
The first and largest eruption, climaxed to the south west of the current park boundaries 2.2 million years ago and formed a caldera about 30 by 50 miles in size and hundreds of metres deep after releasing 2,500 cubic kilometres of material (mostly ash, pumice and other pyroclastics). This caldera has been filled-in by subsequent eruptions and the geologic formation created by this eruption is called the Huckleberry Ridge Tuff. The second eruption, at 280 cubic km of material ejected, climaxed 1.2 million years ago and formed the much smaller Island Park Caldera and the geologic formation called the Mesa Falls Tuff. All three climax eruptions released vast amounts of ash that blanketed much of central North America and fell many hundreds of miles away (as far as California to the southwest; see Lake Tecopa). The amount of ash and gases released into the atmosphere probably caused significant impacts to world weather patterns and led to the extinction of many species in at least North America. About 160,000 years ago a much smaller climax eruption occurred which formed a relatively small caldera that is now filled-in with the West Thumb of Yellowstone Lake.
After the last major climax eruption 630,000 years ago until about 70,000 years ago, Yellowstone Caldera was nearly filled-in with periodic eruptions of rhyolitic lavas (example at Obsidian Cliffs) and basaltic lavas (example at Sheepeaters Cliff). But 150,000 years ago the floor of the plateau began to bulge-up again. Two areas in particular at the focci of the elliptically-shaped caldera are raising faster than the rest of the plateau. This differential in uplift has created two resurgent domes (Sour Creek dome and Mallard Lake dome) which are uplifting at 15 millimetres a year while the rest of the caldera area of the plateau is uplifting at 12.5 mm/yr.
Preserved within Yellowstone are many geothermal features and some 10,000 hot springs and geysers, 62% of the planet's known total. The super-heated water that sustains these features comes from the same hot spot described above. The most famous geyser in the park, and perhaps the world, is Old Faithful Geyser (located in Upper Geyser Basin) but the park also contains the largest geyser in the world, Steamboat Geyser (in Norris Geyser Basin; see Geothermal areas of Yellowstone).
Tourist information
Yellowstone is one of the most popular national parks in the US.
The park is unique in that it features multiple natural wonders all in the same park.
You can find geysers, hot springs, a grand canyon, forests, wilderness, wildlife and even a large lake inside the park. Due to the diversity of the features in the park, the list of activities for visitors is nearly endless. From backpacking to mountaineering, from kayaking to fishing, from sightseeing to watching bison, moose, and elk wandering into the parking lot of the visitor centers, most visitors enjoy a memorable experience in nature.
Due to the geothermal activities of the park, the odor of sulfur is common around the park.
Visitors with respiratory difficulties should consult their doctors before visiting.
Wildland fire is common in the park. One major wildfire in 1988 burnt down much of the forests in the park. It would be wise to check the status of the park before planning a trip.
Visitors may stay right in the park, with a clear view of Old Faithful Geyser, at the park's Old Faithful Inn.
References
- Geology of National Parks: Fifth Edition, Ann G. Harris, Esther Tuttle, Sherwood D. Tuttle (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7
- National Park Service [1]
- Yellowstone Park Foundation [1]
External link