After two powerful earthquakes that occurred in California, the number of search queries for the Yellowstone Caldera and Supervolcano increased. Although tremors arose in a completely different place in the United States, many Americans (and other people around the world) were seriously concerned that seismic activity could provoke an eruption, which supposedly could destroy the entire country and create a volcanic winter on Earth. Lenta.ru tells you how justified these fears are and what real dangers can be hidden in Yellowstone.
Experts, including experts from the US Geological Survey, assure that these super-rebellion fears are completely groundless. According to geologists, earthquakes of magnitude 6-7 occur quite often in the western part of the North American continent. Since 1900, about a hundred earthquakes with a magnitude of more than six and nine earthquakes with a magnitude of more than seven have occurred throughout the United States (these figures are increasing if we consider Mexico and Canada). Most of the aftershocks occur in California, but the aftershocks also affect the states of Oregon, Washington, Nevada, Utah, Idaho, Montana and Wyoming. On the territory of the last three states is just Yellowstone National Park.
Yellowstone Supervolcano has not erupted for 70 thousand years. The last time was a massive outpouring of magma, not a catastrophic explosion. For all this time, according to simple calculations, there were about seven thousand earthquakes of a magnitude greater than seven. At the same time, none of them caused eruptions. Caldera did not explode in 1992, when the Landers earthquake occurred in Southern California (M7.3), and in 1999 with an earthquake in the Hector mine in the same region (M7.1). Moreover, tremors did not provoke eruptions of other volcanoes, including the Long Valley supervolcano, which was much closer to the epicenter of seismic activity than Yellowstone is now.
The very proximity to Yellowstone does not matter. In 1959, an earthquake on Lake Hebgen (M7.3) occurred right on the border of Idaho and Montana, on the western edge of Yellowstone National Park. Supervolcano did not wake up.
At the same time, experts recognize that tremors affect volcanoes – but they do it in an unobvious and non-dramatic way. The Landers and Hector earthquakes caused weak seismic activity (magnitude less than one) in the Long Valley caldera. An earthquake in Alaska in 2002 (M7.9) provoked rock fluctuations in the area of many volcanoes in the USA: Mount Rainier, Long Valley and Yellowstone. Such a connection is detected on the basis of data indicating that weak earthquakes occur with the arrival of seismic waves from a distant epicenter.
According to geologists, there may be several causes of secondary earthquakes. It is possible that seismic waves cause liquid media coming from igneous reservoirs to move underground, destroying rocks. Another explanation is the increase in fluid pressure in hydrothermal systems, in which the pressure is already at a critical level. As a result, microcracks and weak earthquakes occur. It is possible that both scenarios are often implemented.
Strong seismic activity affects hydrothermal systems such as geysers. The earthquake on Lake Hebgen caused 289 springs to erupt as geysers, 160 of which were not geysers. The Alaskan earthquake in 2002 changed the modes of operation of some geysers.
Nevertheless, Yellowstone is indeed a real danger – but not exactly the kind that many news articles, websites, documentaries and video clips speak of. Hydrothermal explosions are the most urgent threat when overheated and under high pressure water breaks out to the surface with a large number of rock fragments to form a crater.
On average, a yellow hydrothermal explosion occurs every two years in Yellowstone. In 1989, the Porkchop geyser exploded, and pieces of stones were scattered at a distance of 66 meters from the source. Although the probability of human victims during such events is very small, it is worth remembering that such phenomena are extremely unpredictable. Geyser Steamboat, for example, in the past few years, breaking records in frequency of eruptions.
More often, people are dying who neglect safety rules and go off special paths in order to approach the geyser. The crust covering the hydrothermal springs is very fragile and cannot withstand the weight of a person; you can fall into boiling water.
Powerful earthquakes (with a magnitude ranging from seven) are considered the second most likely danger of Yellowstone, where there are many faults. Approximately a couple of thousand aftershocks occur every year, but 99 percent of them have a magnitude of two or less and are not felt by people. Within the caldera, the magnitude of seismic activity can be as high as six due to the nature of the rocks and fractures. Outside the giant crater, earthquake power may be higher due to the expansion of the volcanic basin and ridges. The catastrophe on Hebgen Lake in 1959 led to a huge landslide and partial destruction of the dam. As a result, 28 people died. However, such events do not occur more than twice a century.
As for the direct eruptions of Yellowstone, the latter of them were outpourings of magma flows with moderate emissions of volcanic ash. Individual streams of rhyolitic lava in the National Park are among the largest on Earth. At length they reach 30 kilometers, and in thickness – more than 400 meters. Such eruptions occurred in groups, one after another, separated by long periods of calm. The last of them happened 70 thousand years ago and formed the Pitchstone Plateau. Rhyolite lava filled most of the caldera, with a total flow of 600 cubic kilometers.
Therefore, if a new super-hardening takes place in the future, it will lead to a lava flow and, less likely, to moderate ash precipitation. Now we live in a break between eruptions, and monitoring data show that the volcanic activity in the caldera does not increase.
The least likely disaster and worst case scenario is an explosive eruption, but the chance that this will happen is one in a million. Someday in the future – in tens of thousands of years – such a super-inculcation on Earth can happen, but it is not necessary that it ever happen in Yellowstone.