Caldera, which lies at the heart of Yellowstone National Park, is the tip of a huge volcano, which is in turn, bound to a hot spot. This is a fixed point within the earth's crust, where hot magma rises to the top. This accumulates below the earth's surface, thereby forming an underground magma chamber. The rocks lying at the surface of the magma chamber, raise out from under the high pressure of the hot magma and crack. If the magma rises explosively in these cracks to the surface, the volcano erupts. With the explosion, the roof of the magma chamber breaks and forms a caldera.
While the hot spot is firmly anchored in the earth's crust, the North American plate moves across this hot spot. This results in volcanic tracks arranged in a line, which trace the movement of the plate. In the 17 million years in which the Yellowstone volcano has been active, the continent moved some 300 miles across the hot spot. The volcanic resultant testimonies extend from southern Idaho to the craters of the "Moon Lava Field" on the flood basalt layer of the Snake River and to the present Yellowstone caldera.
Today's caldera of Yellowstone National Park was created in the last major eruption of the volcano about 640,000 years ago. Under the caldera is a huge magma chamber located approximately eight kilometres deep, which is now almost filled with lava. The lava comes from smaller eruptions of a period from 630,000 to 700,000 years ago. The magma chamber is about 60 kilometres long, 40 kilometres wide and ten kilometres thick. Therefore, the Yellowstone volcano is one of the world's groups of super volcanoes. It is the largest super volcano on the American continent. The hot magma heats the groundwater seepage in the porous lava rock. This then occurs as hot springs, geysers and mud holes in the earth's surface.
Due to the cycle of about 600,000 to 640,000 years, geologists think an eruption of Yellowstone volcano is likely within the next milennia. The consequences of such an outbreak could assume global proportions. There was a volcanic winter (with an average global cooling of over 3 °C) after the outbreak of the super volcano Toba in Sumatra, some 74,000 years ago.
The existence of the Yellowstone super-volcano, with its huge magma chamber is far from proven. The hot springs do prove volcanic activity, but only the University of Utah seismographic studies have determined the dimensions of the magma chamber. With the help of 22 seismographs, the speed of earthquake waves, which resulted from the frequent earthquakes, was measured. Changes in the rate of rocks provided the necessary data to calculate the size of the magma chamber. The enormous scale of the Yellowstone caldera was first detected on satellite images from NASA.
H. Kiegel; Ü: C. Fleming