ARTHUR L. DAY MEDAL: EXPERIMENTAL VOLCANOLOGY: ACCESSING THE INACCESSIBLE

Volcanic activity on Earth is one of the constants of the Earth System on all timescales of consideration. Despite the increasing monitoring of volcanic systems, an inner view of the physico-chemical processes accompanying eruption remains inaccessible.

Fortunately however, focussing on the mechanistic description of volcanic ascent and eruption drives the challenge before us into timescales of observation that are easily accessible in the laboratory. The moderate pressures extant during most of the deciding transitions in magmatic behavior now pose little obstacle to increasingly sophisticated experimental methods and instrumentation.

As a result, the high speed evolution of magmatic bubbly liquids into dusty gases in explosive fragmentation is revealing its secrets. Quantification of the dynamics of the processes accompanying final ascent of highly viscous magmas and their implications for the seemingly quiescent path of extrusion of silicic lavas versus the violent path of explosion (flow or blow?) now presents us with a picture of the final stages of subvolcanic magmatism that is radically altered from that which existed as little as a decade ago.

Emerging is a view of increasingly complex multiphase fluids whose character is capable of (and may require) switching repetitively between liquid-like and solid-like as a matter of course during shallow ascent. In this behavior may lie a key to the degassing efficiency of lavas ascending in conduits.

In the case of “intact” extrusion the interplay of rheology and viscous heating may control lava advance.

In the case of fragmentation, the auto-reaction of ash and gases may lead to subtle sequestering of significant amounts of magmatic volatiles before the mixture even leaves the conduit.

In either case, the near–surficial state of welding, densifying plugs may yet yield the key to understanding the evolution of porosity and permeability in lava domes and the seemingly unpredictable explosivity of extruded lavas.

By combining an experimental approach with volcano monitoring data and direct observations of recent silicic eruptions, further progress is assured in the coming years.