A team of geologists and geophysicists, led by the University of Geneva, Switzerland, has studied what causes a volcano to erupt and why some erupt regularly, while others remain dormant for thousands of years. They determined that most of the magma rising from depth actually does not cause a volcanic eruption.
Magma is molten rock that rises from tens of kilometers deep to the Earth’s surface. “During its journey, magma can get trapped in reservoirs within the Earth’s crust, where it may stagnate for thousands of years and potentially never erupt,” says Meredith Townsend, a researcher at the Department of Earth Sciences of the University of Oregon.
Eleonora Rivalta, a researcher at the University of Bologna, studied the propagation of magma as it rises to the surface: “If it is runny enough, that it does not contain too many crystals, magma can rise very quickly by a sort of self-propelled fracking,” she continues. If magma crystallizes more than 50%, it becomes too viscous and its marck towards the surface stops.Also, magma can take different paths, vertical, horizontal or inclined.
Luca Caricchi, professor at the Department of Earth Sciences of the Faculty of Science of UNIGE explains,”For an eruption to take place, several conditions must be met simultaneously. Magma with less than 50% crystals must be stored in a reservoir. Then this reservoir must be overpressurised. The overpressure can be the result of internal phenomena such as renewed injection of magma or the exsolution of magmatic gasses or it can rise to critical values because of external events such as earthquakes. Finally, once the pressure is sufficient for the magma to start rising, there are still many obstacles that can prevent the magma from erupting.