Plunge into the piping of one of the most active volcanoes in the world

How does a volcanic eruption ? What Controls Eruptive Style ? Even if knowledge accumulates little by little, understanding volcanic systems requires studying the processes that take place in depth, at the root of the volcanoes. An area that is only indirectly accessible and knowledge of which is therefore still very limited.

The complex architecture of volcanic systems

If all volcanoes function at first sight in the same way, by rising puddles basalts from the partial fusion from coat higher, the styles and frequency of eruptions can be highly variable, not only between different volcanoes around the globe, but also on the same volcanic edifice. This variability is mainly due to the way in which the magma is transported from the depth to the surface. The characteristics of the rise of the magma depend in particular on the thickness and the composition of the continental crustwhich will influence the storage capacity of magma at intermediate levels, its crystallization, its degassingits differentiation as well as the chemical interactions with the surrounding rocks.

Previously, magma was generally considered to be stored in stable tanks located at shallow depth. But more and more studies suggest more complex mechanisms, with in particular the existence of trans-crustal systems: the magmatic reservoirs would thus rather be staggered over the entire thickness of the crust, with a heterogeneous distribution of magma. These different reservoirs would also not be connected to each other permanently, but rather intermittently. The variability of eruptions would therefore be dependent on the interactions evolving over time between these different magma storage zones within the crust. The way in which these magmatic systems are built over time and how they evolve is however still poorly understood, in particular because of the difficulty of imaging the crust at depth.

Tremors to probe the crust

However, researchers have just succeeded in characterizing the deep magmatic system of one of the most active volcanic complexes in the world: the Klyuchevskov volcanic group in Kamchatka, Russia. To study these volcanoes in depth, scientists from the Institut des Sciences de la Earth from Grenoble, as well as their Russian colleagues, used the seismic activity produced by the volcanoes themselves. These small jerks are called “tremors”.

The pressure exerted by the magma within the magmatic system indeed varies according to time. These stress variations generate a wide variety of seismic activity, which can be measured. These can be transient signals or small jerks, tremors, that last for long periods of time. By definition, these tremors are associated with active parts of the magmatic system. Their analysis thus makes it possible to image the dynamics of the volcanic system in space, but also to follow its evolution over time.

The volcanic system is stepped throughout the thickness of the crust

The researchers thus monitored certain volcanoes located on the Russian peninsula of Kamchatka. It is one of the largest and most active volcanic complexes in the world. The volcanic activity here results from the subduction of the Pacific plate under the peninsula.

The results of the study, published in Science Advances, show that the active magmatic system is staged over the entire thickness of the crust. The system would have its source at the base of the crust, at the level of the moho (about 30 kilometers deep) and would branch upwards to feed several volcanoes through different conduits. The magmatic system could thus extend horizontally over great distances. Thanks to the analysis of tremors, researchers can thus define the active zones of the system, and this over the entire height of the crust and follow their evolution over time. The existence of “traffic jams” could temporarily prevent the magma to progress, causing the pressure to increase locally until rupture. This process would lead to the transient activation of the different zones.

The data obtained on the volcanoes of Kamchatka could help to understand other large volcanic systems.