As scorching magma rushes to flood a volcano’s subterranean chamber like in Yellowstone, the volcano becomes heavier and its gravitational pull increases. Similarly, the effects of gravity around a volcano are weekend when the magma chamber empties or is drained of molten rock. US Geological Survey (USGS) scientists who keep a watchful eye on Yellowstone volcano, believe this could be an essential tool in monitoring volcanic activity. The average gravitational pull or gravitational acceleration around the globe is a steady 32ft per second squared (9.8m per second squared).
But the so-called gravitational constant is not a constant at all and will change depending on your elevation and the ground you are standing on.
For instance, a Mount Everest climber weighing 68kg at sea level will only weigh 67.8kg at the mountain’s summit.
According to Michael Poland, chief scientist at the USGS, local geology has an impact on gravity due to the makeup and density of rock.
The scientist explained in this week’s issue of the Caldera Chronicles: “If there is a very dense deposit of copper beneath the surface, for example, the gravitational pull will be stronger than if the subsurface was made up of, say, uncompacted soil.
“Measuring the gravitational pull at the surface of the Earth can therefore tell you something about the composition of the subsurface.”
The differences in gravitational pull might be too little for people to notice but Dr Poland said specialised equipment deployed around Yellowstone volcano can pick out tiny spikes and drops.
These machines, known as gravimeters, use a very sensitive spring to calculate the gravitational acceleration acting on a weight attached to the spring.
If the gravity within a specific part of the park is on the rise, the spring becomes lower as it is dragged down.
If the gravity is dropping, the spring, in turn, shortens in length.
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Gravimeters, though simple, are an “excellent tool” for measuring future volcanic activity deep beneath the surface of Yellowstone.
Dr Poland said: “Because variations in shallow water levels and other seasonal factors are relatively small, it should be possible to ‘see’ any changes caused by magma.
“In the future, Yellowstone Volcano Observatory will conduct annual gravity measurements in the caldera area to assess magmatic activity, combining those results with insights from deformation, seismicity, gas emissions, and thermal changes.”
The announcement comes after USGS scientists in collaboration with the Royal Netherlands Meteorological Institute, conducted a series of gravity measurements in 2017.
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The results of the study were published on March 28, this year, in the Journal of Geophysical Research.
The geologists have found the movement of groundwater levels and hydrothermal activity have not had any additional effect on Yellowstone’s gravity.
Overall, past gravity surveys within Yellowstone have not yielded any worrying results.
Dr Poland said this might be the result of Yellowstone’s magma being relatively deep beneath the ground – about 3.1 miles down (five kilometres).
The deeper the magma is, the smaller the effect it will have on gravity.
