Seismologists at UNAVCO, a non-profit university consortium, use data from the Global Positioning System, inclined goniometers and strain gauges installed in deviated wells to continuously monitor the slightest deformations of the solid rock covering the Yellowstone magma chamber.
Scientists are not able to see the magma itself, but by registering magmatic gases released to the surface and continuously monitoring surface deformations, they can suggest the course of certain processes deep in the depths. Experts today warn of dramatic changes in the parameters they observe, which may be a direct consequence of the increase in pressure in the magma chamber.
In an article for the popular science publication Billings Gazette, David Mancin and Glen Mattioli, surveyors with UNAVCO, write:
To detect deformation within the subsurface, scientists measure the change in diameter or volume of a strain gauge, an extremely sensitive instrument that is continuously poured into the well. In Yellowstone, strain gauges are installed 100 to 250 meters (328 to 820 feet) below the surface. Downhole strain gauges can detect deformation changes of the order of four picometers. This is about one ten millionth the width of a human hair, a distance comparable to the size of a hydrogen atom!
Sometimes these tiny strain measurements come as big surprises. For example, Yellowstone strain gauges are sensitive enough to register surface waves on Lake Yellowstone, which is 12 miles from the sensors!
Even more strain gauges can tell you about the behavior of magma. It's not that Yellowstone magma affects the strain gauges directly, but rather the magma in the crust affects how waveforms are measured on the strain gauges. At this point, the deformation signal of solid rocks is much greater than would be expected if the cover over the caldera were completely solid.
It is unlikely that the magma began to melt the shell surrounding it. Rather, we are talking about a semi-melt, when liquid rock, which is about 5-15%, occupies small cavity pockets in the spaces between the solid rock.
Promotional video:
Computer simulations show that the magma zone beneath the caldera enhances wave motion - which is exactly what the strain gauges measure. These independent observations are consistent with other Yellowstone instruments, such as seismometers, which indicate a zone of semi-molten rock beginning about 3 miles below the surface.
At the end of the article, experts reassure the public by promising that if Yellowstone will explode, it will not be earlier than 300,000 years, since it usually erupts every million years, and the last eruption was 700,000 years ago.
However, if this volcano did explode, about 87,000 Wyoming's people would be killed immediately, and two-thirds of the United States would immediately be rendered uninhabitable. Ashes from the volcano will enter the atmosphere, blocking sunlight, which will directly affect life all over the planet, making everyone a "nuclear winter".