A team of US geologists from US Geological Surveyin collaboration with researchers at Oregon State University and other institutions, found that under the Yellowstone volcano calderain Wyoming (United States), are present at least seven magma reservoirs containing approximately 400 km3 of magma. The magma type rhyolitic, which fuels explosive eruptions, has accumulated especially in the north-eastern area of the caldera, away from areas where past eruptions have occurred. The discovery was possible thanks to details geophysical investigations. The north-eastern area could therefore be there future main site of volcanic activity at the caldera. In the past, the Yellowstone volcano has given rise to very violent eruptions, which however are not expected to be repeated for hundreds of thousands of years. However, more modest eruptions could occur in the meantime, so knowing where the magma is accumulating is very important.
The Yellowstone caldera and its eruptions
The so-called “supervolcano” of Yellowstone is one of the largest in the world and is made up of a series of calderashuge depressions extended overall approximately 3900 km2originating from the very violent ones explosive eruptions which have affected the area in the past. This volcanic activity is due to the presence of a hot spotor hot spotsthat is, a narrow and relatively fixed area in correspondence with which columns of magma (called plumes) coming from the mantle. This hot spot has fueled countless eruptions throughout history: one of the most intense took place 2.1 million years ago and emitted such a quantity of material as to cover an area covering more than 2450 km2. The Yellowstone volcano, whose last eruption (of the effusive type) dates back to 3300 years ago, is considered a active volcano: the intense testify to this secondary volcanic phenomenasuch as geysers and fumaroles.
The new study on the distribution of magma under Yellowstone
In recent years, the Yellowstone volcano has been the subject of studies aimed at determining the chemical composition of the magma and the volume it occupies in the magma chamber. In the new study, researchers from Oregon State University identified the distribution of magma underground thanks to details geophysical techniquessuch as seismic tomography and a magnetotelluric survey. They thus discovered that they are present under the caldera at least seven areas with high magma contentsome of which are powered by the others. These magma reservoirs are located at depths between 4 and 47 kilometersup close to the boundary between crust and mantle. In their lower portion is located basaltic magmawhich gives rise to effusive eruptions, in the upper one rhyolitic magmaresponsible for the most violent explosive eruptions. The researchers also managed to estimate the amount of magma present underground, equal to approximately 388-489 km3 and distributed unevenly. Most rhyolitic magma is found in the northeastern area of the calderafar from where past eruptions have concentrated.
Why the new study on the Yellowstone magma chamber is important
Knowing the chemical composition of the magma that accumulates at depth is important because the type of eruption that could occur in the future depends on it. In the past, the Yellowstone volcano gave rise to explosive eruptions that created calderas, alternating with smaller effusive eruptions. The volume of magma identified by the researchers under the caldera is notable: that present in the north-eastern area, of rhyolitic type, is comparable to that released during the smallest of the eruptions that originated the caldera. However, studies to date have determined that Yellowstone’s most violent eruptions do occur approximately every 600,000 years (and according to the most recent research even up to 1.5 million years), which is why the discovery should not be a cause for alarm. However, the volcano is constantly monitored, for example by recording earthquakes and deformations in the area.
