There is something fascinating and mysterious about the figure of any volcano. The disruptive force with which it manifests its presence, alternating with periods of quiescence where it takes on an "innocent" aspect, make a volcano an extremely interesting object to study.
If you then add detection systems ad infrasound, alignments of theEarth axis with the polar one and above all if unsuspected links of cause – effect in the volcanic activity of these "giants of nature" are discovered, then things get even more interesting. In this regard, new research has been concerned with investigating the effects of the earth's rotation on the activity of a volcano known to us: Etna.
A fact
The research starts from a fact: seismic activity and magma explosions in the area surrounding Etna seem to increase significantly when the Earth's rotation axis is found to be more inclined than the Earth's geographical axis . What are we talking about? The rotation axis of the Earth is not always perfectly coincident with the straight line that passes through the ice regions called "north pole and south pole".
In short, the geographic poles often revolve around the axis of rotation of the earth, and the effect is obviously appreciable only when viewed from space. Every 6.4 years, the axes align and the oscillation subsides for a short period, at the end of which the geographic poles move away from the rotation axis and start their spiral motion again.
The following video will clear up any doubts. The animation shows the Earth's rotation movement and that of the Earth's rotation axis (in orange) with respect to the geographic north and south poles (shown in blue). Caution: don't confuse the effect just described with the effect of terrestrial axis precession, which is a millennial movement and which is not included in this discussion.
With the passage of time, the geographic poles seem to move away from the rotation axis when viewed from space and then back again. Obviously the size and speed of the spiral are deliberately exaggerated.
The phenomenon is driven by climatic changes due to the passing of the seasons, the melting of the polar ice caps and the movement of the tectonic plates. This "polar movement" causes the deformation of the earth's crust over seasons or years. Distortion occurs with greater intensity towards i 45 degrees latitude, where the crust moves about 1 centimeter per year.
A study published in the journal Geophysical Research Letters suggests that polar movement and subsequent shifts in the earth's crust may increase volcanic activity. In practice, a nice analogy seems to be found: just as the climate is capable of influencing the earth's rotation, the earth's rotation can influence volcanic activity and seismic phenomena.
Not really good news
These new findings, however, do not allow scientists to improve predictions about volcanic activity. Although the study suggests that earthquakes may be more common or that volcanic eruptions may expel more lava when the distance between the Earth's geographical and rotational axis is at its maximum, we find ourselves faced with a problem of time scale: the time interval that characterizes these phenomena is too large to be able to draw up a model and obtain significant short-term forecasts.
But the fact remains that the results indicate an interesting assumption: it is the first time that some relationship has been found between two apparently unrelated terrestrial phenomena. Researchers explain phenomenology as a "continuous accumulation of small displacements"which adding up over a long time can lead to phenomena that are then clearly measurable (such as the intensity of a volcanic explosion).
When the Earth trembles
In the study in question, Sébastien Lambert, geophysicist at the Paris Observatory in France, and his colleague Gianluca Sottili, a volcanologist from the Sapienza University of Rome in Italy, focused on Etna because the volcano is well studied, which means that there is a lot of data available and then because it is just over 45 degrees latitude. There were also no volcanic crises out of the ordinary during the observation period, which could otherwise have masked the "traces" of polar motion.
Lambert and Sottili used the seismic recordings of 11,263 earthquakes that occurred within 43 kilometers from the summit of Etna between 1999 and 2019. The team also used records of the amount of magma exploded by the volcano since 1900. They included 62 eruptions in the analysis.
The two therefore have compared the distance between the geographic and rotational poles at the time it occurred each event to determine if volcanic activity was connected to the earth's rotation.
Lambert and Sottili they discovered that there were multiple earthquakes when the Earth's rotation pole was further away from the geographic axis. Between 1999 and 2019, these peaks occurred in 2002 and 2009.
The search could then one day continue towards the volcanoes of the Pacific and the Atlantic. Examine the volcanoes of the Belt of Fire to see if the rotation of the Earth affects their activity would certainly be interesting, considering that they cover different latitudes. And maybe, why not, extend these laws to other planets with an alleged volcanic activity below the surface.
Develop more efficient alarm systems?
Over the years, scientists have developed an automated alarm system for volcanic eruptions, with almost instantaneous activation. The new system could help state officials to warn the population and bodies set up in time to take action. There is research published in the Journal of Geophysical Research: Solid Earth, a journal of the American Geophysical Union, which details this new alarm system. The authors of the study tested this system for eight years on Etna, our volcano which is also highly regarded abroad.
The effectiveness of this alarm was proven in the field in 2015 when the Italian government managed to activate an emergency plan about an hour before an eruption, all thanks to the reporting of this automated system. We can consider ourselves privileged, because not all volcanoes enjoy such a level of observation.
Most of the approximately 1,500 active volcanoes worldwide are not monitored in real time. Many volcanoes are monitored with seismic wave-based methods, which are vibrations of the Earth's mantle layers that can be triggered by eruptions. However, these measurements always require interpretations by volcanology experts and only after this phase are the alarms issued.
57 out of 59 eruptions
Scientists are moving to optimize these procedures: volcanoes, during their eruption processes, generate low frequency sounds that are not audible to humans, these waves can travel thousands of kilometers and are less equivocal than seismic waves. The researchers listened to the sounds produced by Etna for years with infrared sensor systems located 6 kilometers away from the volcano.
They found that infrared sensors can reliably identify the signs of a rash. From 2008 to 2016, sensors correctly detected 57 of 59 eruptions and sent alerts to researchers about an hour before each eruption. For the past four years, the automated system has remained operational in monitoring Etna and has issued warnings without error.
To extend the benefits of automatic alerts to the rest of the world, however, researchers need to study infrasound from other types of volcanoes. The first eruption phases of Etna, which allow early warnings, may however be shorter or completely absent in volcanoes with different geological characteristics.
The idea to create a global alarm system would be to use a much denser set of sensors to monitor several volcanoes simultaneously over long distances. All this opens up a new way of monitoring volcanoes on a global scale, and it is needless to emphasize how this can, in many cases, make the difference between life and death.
