Bisons im Yellowstone
One of the most fantastic natural attractions in the world is located in the USA: Yellowstone National Park. Nowhere else on earth are there so many hot springs, colourful water pools and geysers. Furthermore, Yellowstone National Park is an El Dorado for nature lovers.
Again and again, Yellowstone National Park appears in the media, mostly as a dark bringer of the apocalypse. In movies gigantic eruptions can be seen and pyroclastic flows devour everything.
In fact, the natural phenomena of the national park hide a geological history that is more exciting than any crime thriller. Beneath Yellowstone lies a super volcano that has the power to destroy civilization.
History of Yellowstone National ParkYellowstone National Park is the oldest national park in the world. It was founded in 1872 and protects an idyllic landscape with dense coniferous forests, lakes and rivers from human exploitation. The park, which is also the largest national park in the USA, offers shelter to many endangered animal species: Bears, moose, pumas, lynx, wolves and of course the bison feel at home on the high plateau in the Rocky Mountains. For a long time the remote area was safe from the white settlers: it was not until 1807 that the area was discovered by the trapper John Colter. Until then, Indians from the Minnetaree tribe lived here. They called the area "Mi tse a-da-zi", which translated means "yellow river rock". Possibly this name is an allusion to gold findings in the water of the Yellowstone River, but also sulphur, or yellow tuffs can be the reason for the name.
Colter's reports were not well received at the time. It was not until 1859 that the geologist Ferdinand V. Hayden organized an expedition into the area, but failed shortly before Yellowstone due to an early onset of winter. It was not until the Folsom expedition of 1869 that scientific reports and photographs were provided, which encouraged Hayden to undertake a second expedition. His reports on the undestroyed nature, the rich fauna and many other, even more amazing wonders of nature prompted the Senate to put the area under protection. Many of the animal species living in the Yellowstone area were already endangered at that time; the gold rush had also devastated entire areas.
The Yellowstone CalderaThe natural phenomena the geologist was able to report proved to be the world's largest collection of hot springs, colourful water basins, mud holes and geysers. Early on, a volcano in Yellowstone was suspected to be the cause of these phenomena, but was not discovered for a long time. Only satellite images revealed the secret of Yellowstone National Park: the 10,000 or so hot springs and geysers are embedded in a huge caldera so large that its structure cannot be seen from the ground; it measures 40 x 25 kilometres and is characterised only by a relatively shallow depression. It is mostly filled up with lava flows from smaller eruptions and with sediments from the surrounding mountains.
The super volcano eruptionsFirst eruptions in the area of Yellowstone National Park took place 2.1 million years ago. 200,000 years later, this phase of activity reached its peak in a supervolcano eruption, during which a first caldera was formed. 1.2 million years ago, the Yellowstone volcano entered a new period of activity. In another supervolcano eruption, the Mesa Fall tuffs were mined, covering an area of 280 square kilometres. Another caldera was created. After that the Yellowstone volcano was dormant for a long time.
The most recent supervolcano eruption occurred about 640,000 years ago. It produced 1000 cubic kilometres of material and deposited the lava creek tuffs; these rhyolites cover an area of 340 square kilometres. As with previous large eruptions, the final eruptions did not happen in one fell swoop; they were announced long before with a series of smaller eruptions. In the final stage of the eruption the youngest caldera formed. After the supervolcano eruption, again thousands of years passed with only little activity. Lava flows filled the caldera during this time.
The volcanism is caused here, in the middle of a continent, by a hot spot. The calderas all lie in a row, indicating that the North American continent has migrated across a stationary magma bubble. Unlike oceanic hot-spot volcanoes, Yellowstone produces predominantly rhyolitic magma. Rhyolite is typical of subduction zone volcanoes and in fact, the mantle plume beneath Yellowstone promotes acidic magma that originated beneath the North American continent through the melting of the Pacific plate. Some smaller eruptions have also produced basaltic lava.
The three calderas overlap each other, and the largest of them, formed during the first eruption, measures 80 x 55 kilometres. The three activity cycles average 600,000 years each, which is about the same period of time since the last eruption.
Eruptions since the last super volcano eruptionsUSGS scientists reconstructed the eruption history of the last 640,000 years. Since the last supervolcano eruption and the formation of the latest caldera, there have been about 80 volcanic eruptions. Most of these eruptions were effusive and their effects were limited to the immediate vicinity of the volcano. There have been 27 rhyolitic lava flows inside the caldera and 13 outside the caldera. Besides rhyolite, basalt was extracted from 40 vents. These vents are also located outside the caldera. Some explosive volcanic eruptions were comparable in strength to Pinatubo in 1991. The most recent volcanic eruption in Yellowstone occurred 70,000 years ago and produced a lava flow on the Pitchstone Plateau. Since then the volcano has been in a post-volcanic stage.
Current development in Yellowstone calderaSpeculation in the media about an imminent supervolcano eruption is increasing; this speculation is fuelled by strong movements of the caldera floor. In fact, since 2004, magma appears to have been flowing into the magma reservoir below Yellowstone, raising the ground in places by about 25 cm. These soil deformations are particularly strong at the bottom of Yellowstone Lake and in the Norris Geyser Basin, where a number of new hot springs with enormously high temperatures have also been created. The rear part of the Norris Geyser Basin has been closed to visitors. The bulge and the increased heat flow are caused by a magma intrusion at a depth of 10 km and are not signs of an imminent eruption. Volcanologists refer to this form of activity as magmatism. If a volcanic eruption should occur in the next few years, it does not necessarily have to be a supervolcano eruption, more likely a normal eruption. A new study by Girad and Stix (MSU 2012) shows that there are 3 zones in the caldera where future eruptions of different types are very likely to manifest themselves. The first zone is dominated by large fault zones. Here explosive eruptions are most likely to produce large amounts of rhyolitic lava. The second zone is located between the Norris Geyser Basin and Mammoth Hot Springs. An eruption there would probably be phreatomagmatic, or phreatic in origin. The 3rd potential eruption zone is crossed by small fault zones. ...where researchers expect basalt lava flows to erupt. No scenario in the near future assumes a supervolcano eruption.
Geysers and hot springs in Yellowstone N.P.Hot water phenomena such as geysers, hot springs and mud volcanoes are mainly found in the Geyser Basins. These structures owe their existence not only to the hot bedrock of Yellowstone National Park, but also to ice-age deposits that accumulated in the basins' depressions. Glacial moraines created a water-storing layer here; geothermal heat rising from the magma chamber below Yellowstone heats the water, and steam pressure drives it back to the surface.
The most famous geyser in Yellowstone National Park is Old Faithful. It is located in the "Upper Geyser Basin" and was long considered the most reliable geyser, as it erupted in an interval of 91 minutes. This interval has shortened in the last years and Old Faithful does not jump as reliably as before. However, the actual time interval between two eruptions has varied in the past. During an eruption, Old Faithful pumps up to 32,000 liters of water, and its fountain can rise up to 55 meters.
A remarkable geyser of the Upper Geyser Basin is the Castle Geyser. The beautiful travertine cone, which looks like a castle, is said to be about 5000 years old. It erupts at intervals of 10 to 12 hours and produces a water fountain that can reach a height of 27 meters. The water is ejected for about 20 minutes at a time, followed by an eruption phase of about the same length, during which mainly steam is ejected.
Other well-known and beautiful geysers in Yellowstone include the Grand Geyser, which produces the highest regular erupting water column, and the Riverside Geyser on the banks of the Firehole River.
Of the colorful pools of water, Grand Prismatic Spring is the most impressive spring in the entire park. The 91-meter-wide "blue eye" is surrounded by an orange ring of algae on its banks.
The Norris Geyser Basin is home to the geyser, which produces the world's highest water fountain: the fountain of the Steamboat Geyser shoots up to 130 meters high. In return, this geyser pauses between its individual eruptions for several years.
Recent events in Yellowstone calderaIn March 2018 a special phase of activity of the Steamboat Geyser began. Until September of that year it jumped 17 times. Such a jump series has been unprecedented so far. However, volcanologists did not see a general increase in activity in the caldera and attributed the unusual activity of the geyser to a local change in the hyrdothermal system. In September, another relatively unusual event occurred: first, Ear Spring, a normal hot water spring in the Upper Geyser Basin, jumped, and then a crack opened under a jetty near Old Faithful. One of the cracks widened into a new spring.
Yellowstone Natinal Park, doomsday and the mediaFrom time to time, media reports about an impending volcanic eruption in Yellowstone appear. These reports are mainly due to the fact that the ground beneath the Yellowstone caldera has been bulging since 2004 (see above). Nevertheless, media reports about Yellowstone volcano are often overdramatized, especially since a supervolcano eruption is statistically overdue. However, one should not underestimate the geological time frame. A few thousand years do not play a major role here. Moreover, volcanoes do not stick to statistics.
Especially in connection with the supposed end of the world in 2012, the Yellowstone volcano appears in the media. Serious scientists agree, however, that the end of the Mayan calendar is not synonymous with the end of the world. Films like "Supervolcano" and "2012", in which a Supervolcano eruption of Yellowstone plays computer-generated leading roles, have also contributed to the Yellowstone hysteria.
Some geoscientists have an aversion to the term "Supervolcano" because it is a new word that first appeared in media reports. Other scientists have adapted to the circumstances and provided a definition for a supervolcano eruption.
Yellowstone and tourismEvery year more than 3 million people visit the national park. The infrastructure is correspondingly well developed. In the park there are several lodges with restaurants and shops as well as camping sites. These are the cheapest possibility to visit the park for several days. At the same time, the camper is in the middle of the nature; a great experience to sit in the evenings at the campfire and listen to the voices of the forest! With a special permit, it is also possible to go on hikes with a bivouac in the hinterland. The thermal areas are accessible via wooden footbridges. Leaving the footbridges is prohibited, as is gold mining. Beware of bears and bison!
©Marc Szeglat 2006. Last updated 2019.