At Ischia, magma’s journey may matter more than its storage for eruption style

A study of contrasting eruptions at Montagnone found similar temperatures and volatile contents before the magma erupted.

Editorial illustration — not from the study.

Researchers studied trachytic magmas from Montagnone, a volcanic edifice on Ischia in southern Italy, including eruptions that produced lava domes and explosive activity of varying intensity. They examined mineral growth patterns, trapped melt and volatile contents to reconstruct conditions before the eruptions.

The samples showed little variation in the minerals’ compositions and no meaningful differences in pre-eruptive temperatures or volatile contents between the contrasting events. Differences in crystallisation in the magma’s groundmass instead point to changes during ascent as a possible influence on whether the eruptions were explosive or effusive.

What the magma records show

Feldspar and clinopyroxene crystals showed only minor compositional differences within and among the eruptions. Their patterns indicate a magma system shaped mainly by crystal growth and periods of partial crystal dissolution, with little evidence that less-evolved magma entered the system before the eruptions.

The study found that pre-eruptive temperatures and volatile contents were indistinguishable across the events, even though some eruptions were explosive and others formed lava domes. Differences in groundmass crystallisation suggest that the magma’s ascent dynamics—the processes affecting it as it moved through the volcanic conduit—played a key role in controlling eruption style.

Why ascent matters

The results suggest that conditions in a magma reservoir alone may not explain why eruptions from the same volcanic system become explosive or effusive. For hazard assessment, the study supports combining evidence about magma storage before an eruption with evidence about processes occurring as magma rises toward the surface.

Evidence and limits

The researchers inferred magma conditions from feldspar and clinopyroxene zoning, apatite inclusions and volatile measurements in melt inclusions, along with differences in groundmass crystallisation. These mineral and chemical records provide evidence about both pre-eruptive storage and ascent, but the proposed role of ascent dynamics is an interpretation of the observed patterns rather than a direct measurement of magma flow during the eruptions. The study focuses on trachytic eruptions at Montagnone, so its relevance to other volcanoes and magma types remains to be established.

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