Influence of Non-Newtonian rheology on magma degassing

TL;DR

This study demonstrates through laboratory experiments that non-Newtonian magma rheology alone can cause diverse volcanic degassing behaviors, including spontaneous switching between bubbling and channeling regimes, depending on rheological properties.

Contribution

The paper reveals that non-Newtonian rheology of magma can independently induce complex degassing patterns, highlighting its importance in volcanic eruption dynamics.

Findings

Critical flow rate Q* triggers regime switching.

Q* decreases with increasing gas volume fraction.

Non-Newtonian properties influence degassing behavior.

Abstract

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) {\phi}. When {\phi} increases, Q* decreases and the degassing regime changes. Non-Newtonian properties of magma might therefore play a crucial role in volcanic eruption dynamics.