When Bubbles Rise Up

Magma is a three-phase fluid made up of gas, liquid, and solid (crystal) phases. The effect of crystals on bubble rise in magmatic systems has important implications for understanding processes in both volcanic and plutonic systems. Isolde Belien is studying the interaction of a bubble with a crystal suspension, and she is investigating the influence of crystal concentration on the rise speed of bubbles of different sizes.

The rise of bubbles through a crystal-rich magma is simulated in analog experiments with corn syrup and plastic beads, where the beads represent crystals suspended in a melt. Currently, Isolde has looked at the interaction of bubbles with both a dilute and a dense suspension of beads. These beads delay the rise of bubbles, even at very low crystal concentrations. The delay is caused by deflecting the rise path or deforming the bubble around a bead for bubbles that are smaller than or on-the-order of the bead size. The rise time of big bubbles is delayed by beads that interact with the turbulent wake structure of the passing bubble. Layers with high crystal concentration can delay bubbles for long periods of time, effectively trapping small bubbles inside crystal layers. In addition, her experiments show that large bubbles can split upon entering a crystal-rich layer, thus increasing the relative abundance of small bubbles in the system.


Bubble-crystal interactions are further studied by looking at the bubble and crystal populations in tephra. The image below compares analog experiments to a sample of tephra from Stromboli volcano, Italy. Preliminary results of her research challenge conventional interpretations of how bubble/crystal number density relates to conduit processes and eruption style.