Moi, Paul Derand

From time to time I have been exploring volcanology as a hobby and I think that each volcano has its maximal explosivity.

As you know, some volcanoes are explosive and some are effusive because of the content of their magma. It is explosive when it has high silica content lavas that traps all the gases. It is effusive when it has basaltic lavas that have a low silica content and that let the gases escape.

I remarked that explosive volcanoes could have effusive eruptions if the gases were emitted separate from the lava.

So, I chose to create the "maximal explosivity" of one volcano, which is the explosivity of an imaginary eruption for which the gas is separated the less possible from the lava for this volcano (the explosivity of the most explosive eruption possible for this volcano) and for which the volume of magma erupted is maximal for this volcano. For volcanoes which are closely monitored since a long time, it would be possible to measure it (it would be the VEI of the most explosive eruption in historical or prehistorical times).

I also remarked that when a volcano makes a caldera (the collapse of the empty magma chamber after a big eruption), its eruptions are weaker because the volume of its magma chamber decreases. In this way, after a volcano makes a caldera, its maximal explosivity is lower.

To calculate the maximal explosivity of a volcano, I first evaluate the volume of its magma chamber. Then I evaluate the maximal silica content of its magma (magma with no gases separated from the magma and all gases inside the magma). The product of the magma chamber's volume and the maximal silica content of the magma is equal to a largest possible amount of tephra emitted by the largest and most explosive eruption possible for this volcano. With this, it is possible to refer to the Volcanic Explosivity Index scale and get the maximal explosivity of the volcano on this scale...

Beware with subglacial or submarine volcanoes that can have interactions with water in their eruptions: Eyjafjoll is an effusive volcano but its 2010 eruption was explosive due to interaction with water/ice.

See the silica content of the different types of lava:

http://fr.wikipedia.org/wiki/Classification_TAS

See the Volcanic Explosivity Index:

http://fr.wikipedia.org/wiki/Indice_d'explosivit%C3%A9_volcanique