Although volcanologists are getting pretty good at forecasting the start of an eruption, predicting the end is much more difficult.
If a volcano has been extensively monitored for some time, then scientists get to know what its usual activity is like: the quakes it makes when magma or hydrothermal fluids move about; the way it breathes in and out and changes its shape; the sorts of gases it belches out. If one or more of those parameters begin to significantly shift, then it may suggest something bad is approaching.
When sound observations are combined with a decent knowledge of the volcano’s eruptive history, volcanologists can at the very least warn those nearby that an eruption in the next few days or weeks is more probable than it was previously. However, there is no agreement on what defines an eruption’s termination.
Knowing how much magma is available to erupt would be great. Scientists can’t yet see magma shifting below the surface, but they can estimate how much there is. The amount the ground inflates is an indication for how much pressurized magma is ready to burst through, and the seismic noises made by magma breaking through rock can be used to track its movement. If that inflation turns into deflation, then it could be a sign that the magma supply is running dry or losing the pressure required to punch through.
Magma pools close to the surface when it is about to erupt, but the magma supply is fed by molten rock coming from deep reserves. Even if the amount of magma present at shallow depths is determined, measuring limitations mean that the volcano’s plumbing system is often rarely visualized. That means it is practically impossible to know whether the volcano is being continuously supplied with extra magam or if its stores are soon to expire.
It isn’t even as straightforward as fully depleting a volcano’s reserves. Magma can rise but won’t often erupt. Often, it ponds in a reservoir or an extensive network of possible escape routes, either remaining partially molten or freezing solid.
One way these efforts could be accelerated is through machine learning. An AI, fed data from countless past eruptions, may be able to spot these patterns far quicker than a human ever could.
https://gizmodo.com/why-can-t-we-predict-when-a-volcano-will-stop-erupting-1848006734