Sektion für Mineralogie, Petrologie & Geochemie




Frothing at the mouth of the volcano.

During explosive eruptions magma heats up, foams and explodes.


Explosive eruptions – one of nature’s least predictable hazards – often emit huge volumes of volcanic ash, covering entire continents. Yet, we still don’t understand how coherent magma that buoyantly rises through the Earth’s crust explodes to produce the shards of volcanic ash. Indeed, the last two decades of research in LMU’s Earth and Environmental Sciences department has highlighted just how complex these phenomena can prove.
New work by researchers at LMU – in collaboration with the University of Liverpool and colleagues worldwide – and published in the journal Nature, exposes a new mechanism for explosive eruptions at volcanoes. LMU alumnus, Prof. Yan Lavallée, lead a research campaign on the flanks of one of the most persistently active silicic volcanoes on Earth, Santiaguito at the Santa Maria volcanic complex in Guatemala. At this site, regular eruptions every 20-minutes to 2-hours throw clouds of ash into the atmosphere. After a long sampling campaign and lab-analysis, it became clear the textures and chemistry of the volcanic ash could not be explained by any eruption process that has previously been documented.
In the volcanic ash from Santiaguito, streaks and filaments of volcanic glass are inter-mingled in these eruptions in dynamic and chaotic textures. Furthermore, there is evidence that all the crystals have melted and that bubbles have formed, now trapped in the tiny glassy fragments. Prof. Lavallée’ s laboratory experiments showed that identical textures can be formed when two surfaces of the same Santiaguito magma slide along one another at high velocity. This is thought to occur at the edges of the conduit through which magma must move to reach the surface. This inter-disciplinary research group concludes that friction near the edge of magma-filled conduits produces huge amounts of heat, sufficient to re-melt the crystals that have grown during ascent through the Earth’s crust.
Finally, the group noticed that these frictional heating events often result in the magma foaming and frothing. This is because small amounts of water dissolved in the magma, form bubbles rapidly when the mixture is heated by friction. The result is a catastrophic foam growth, which leads to instabilities in the whole mixture and regular explosions. This suggests that the volcanic ash that is often collected is simply the tiny frozen pieces of what was once a foamy region at the edges of the conduit of magma.

Find the original research article at Nature’s website here:

And the article DOI is 10.1038/nature16153
For more details contact Prof. Donald B. Dingwell at LMU,