Y en la corteza, ¿qué ocurre?
And in the crust, what’s going on? The magma can follow a direct path from its source to the surface but often, its path is more complicated. The magma is sometimes found blocked in the crust (< 60 km depth) and accumulates in a magmatic reservoir (or chamber).
- Just like the liquid in a bottle of Champagne, magma contains pressurized dissolved gas. If the magma chamber gets fractured: for example if the pressure in the reservoir becomes too high and it breaks the roof of the chamber), the gas is brutally decompressed and separates from the magma, forming bubbles: this is referred to as “exsolution”.
- In its rapid ascent, the gas drags the magma towards the surface and, just like with bottle the Champagne suddenly uncorked, this is the eruption!
- Sometimes, the magma chamber can be emptied by the most violent eruptions, and its roof can collapse and form a caldera. But this is not always the case…
In most cases, the magma chamber is only partly emptied, and fills with new magma again from a deep source, and stage 1 and 2 repeat again and again.
Observe the inflation and deflation of the Etna volcano, as a consequence of the filling and emptying of the magma chamber!