Influence of non-Newtonian rheology on magma degassing

Thibaut Divoux (1) , Valérie Vidal (1) , Maurizio Ripepe (2) , Jean-Christophe Géminard (1)

1 Phys-ENS - Laboratoire de Physique de l'ENS Lyon
2 DST - Dipartimento di Scienze della Terra [Firenze]

Many volcanoes exhibit temporal changes in their degassing process, from rapid gas puffing to lava fountaining and long-lasting quiescent passive degassing periods. This range of behaviors has been explained in terms of changes in gas flux and/or magma input rate. We report here a simple laboratory experiment which shows that the non- Newtonian rheology of magma can be responsible, alone, for such intriguing behavior, even in a stationary gas flux regime. We inject a constant gas flow-rate Q at the bottom of a non-Newtonian fluid column, and demonstrate the existence of a critical flow rate Q* above which the system spontaneously alternates between a bubbling and a channeling regime, where a gas channel crosses the entire fluid column. The threshold Q* depends on the fluid rheological properties which are controlled, in particular, by the gas volume fraction (or void fraction) φ. When φ increases, Q* decreases and the degassing regime changes. Non-Newtonian properties of magma might therefore play a crucial role in volcanic eruption dynamics.

Domaines: Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]

Thibaut Divoux, Valérie Vidal, Maurizio Ripepe, Jean-Christophe Géminard. Influence of non-Newtonian rheology on magma degassing. 2011. ⟨hal-00593301⟩