The tiny power behind volcanic eruptions

Highly explosive eruptions present a considerable hazard for communities living nearby active volcanoes. These eruptions can produce columns of ash and gas which extend high into the atmosphere, depositing large volumes of volcanic material kilometres away from the volcano. How explosive a volcanic eruption becomes depends on what happens as magma rises through the crust. As it moves upward, crystals and gas bubbles form, which make the magma thicker (more viscous) and increase the chances of an explosive eruption. Understanding what can lead to these types of eruption can provide crucial information for assessing the danger posed to nearby communities.  

A recent study published in Nature Communications, conducted by an international research team led by Dr. Emily C. Bamber at the Institute of Science, Technology and Sustainability for Ceramics of the National Research Council (CNR-ISSMC), investigated the role of nanoscale crystals in explosive eruptions.  

Fig. 1: a and b show volume renderings where only the nanolites were segmented, which occur as subspherical, isolated crystals as well as more irregular shaped aggregates. c and d show volume renderings where also the evolved, Fe-depleted glass around and between nanolites is segmented (highlighted in yellow). The segmentation of the nanolites, matrix glass and evolved boundary layer was performed based on visual inspection of the images and the estimates of ρe. All volume renderings were produced using VGStudio. In c, the rendering has a cut-away section to allow visualisation of the nanolites.

Such crystals, known as nanolites, are <1 micron in size (for comparison, a human hair is 100 microns in diameter) and therefore, difficult to observe using conventional microscopy techniques due to their small size. To resolve and visualise iron and titanium-enriched nanolites, the team used X-ray ptychography on Diamond’s I13-1 beamline. X-ray ptychography is a lensless, phase imaging microscopy technique at the nanoscale, also described as scanning coherent diffraction imaging (CDI).

The study focused on volcanic rocks from the Las Sierras-Masaya region in Nicaragua, the site of two unusually explosive basaltic eruptions: the Fontana Lapilli and Masaya Triple Layer events. Basaltic magma is typically low in viscosity and erupts gently, but these events produced towering ash columns and ejected over a cubic kilometre of material. 

The key to their explosiveness may lie in the nanolites. The researchers discovered that titanium-rich crystals, known as titanomagnetite, form long, uneven clusters that pull iron and titanium from the surrounding magma. This chemical shift creates silica-rich zones around the crystals, which are significantly more viscous. The result is a magma that is up to 1,000 times thicker than normal and is primed to fragment violently as it rises. 

The I13-1 3D images revealed that nanolites don’t just float freely in the magma. They clump together into structures as large as six micrometres, altering both the chemistry and the physical flow of the molten rock.  

This thickening effect, caused by both the presence of solid particles and the chemical changes they induce, makes magma more prone to explosive fragmentation. In the case of the Fontana Lapilli and Masaya Triple Layer eruptions, the magma’s high crystal content, rapid ascent, and relatively cool storage conditions all contributed to its unexpected explosiveness. 

The findings offer a new lens through which to view volcanic hazards. By understanding how nanolites form and behave, scientists can better predict which eruptions might be more explosive, even in volcanoes previously thought to be low risk.