New research published in the journal Science explains a mechanism that helps to resolve a long-standing puzzle: why some volcanoes with gas-rich magma do not erupt explosively. Previously scientists attributed bubble formation mainly to a drop in ambient pressure as magma rises, a process often compared to opening a bottle of champagne. The new work shows that shear forces inside the volcanic conduit can also create and amplify bubbles.
Shear arises because magma flows faster in the conduit centre and slower near the walls. The team found that shear produces bubbles, especially near the walls where deformation is strongest. If these bubbles grow and coalesce deep in the conduit, they can form persistent channels that allow gas to escape early. Gas loss through such channels can keep the magma flowing quietly rather than fragmenting into an explosive eruption.
In laboratory tests the researchers used a viscous fluid similar to molten rock, saturated it with carbon dioxide, and applied shear above a threshold. Bubbles formed suddenly; higher initial gas supersaturation required less shear to trigger bubble formation, and existing bubbles promoted further nucleation nearby. Computer simulations combined with the experiments indicate the effect is important where viscous magma slides along conduit walls and experiences strong shear. The findings explain different outcomes: low-gas magma can still explode if shear makes many bubbles and the magma rises rapidly, whereas shear can also create degassing channels in gas-rich magma and reduce early explosion risk. The 1980 Mount St. Helens eruption began with a slow lava flow that allowed gas escape by shear-produced bubbles, but a later landslide opened the vent, the pressure fell rapidly, and the volcano exploded. The researchers, including Olivier Bachmann at ETH Zurich, say volcano models should be updated to take shear forces in conduits into account for better hazard prediction.
Difficult words
- mechanism — process that explains how something happens
- shear — force that makes parts slide past each other
- conduit — a channel or pipe that magma moves through
- coalesce — to come together and form one mass
- supersaturation — state when more gas is dissolved than normal
- nucleation — the process where new bubbles or particles form
- viscous — thick and slow flowing like liquid
- degassing — the process of gas leaving a liquid or rock
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- How might including shear forces in volcano models change hazard predictions or evacuation decisions?
- What are the possible benefits and risks if degassing channels let gas escape before an eruption?
- How do lab experiments and computer simulations together help scientists understand real volcanic behaviour?
Related articles
AI audio summaries of research can help — and err
Researchers tested Google’s NotebookLM, which turns research papers into podcast-style audio. The summaries were engaging and clearer for teaching, but every audio overview contained mistakes, so the authors advise reading the original papers to check claims.
Band of Holes at Monte Sierpe: an Indigenous accounting system?
New evidence suggests the Band of Holes at Monte Sierpe in southern Peru was part of a pre‑European Indigenous system for accounting and exchange. Researchers used sediment analysis and drone images to reach this conclusion.
Researchers Call for Clear Rules on Gene-Edited Crops in Mexico
Mexican researchers want rules that distinguish gene-edited crops from GMOs. They launched a petition asking the government for evidence-based regulation while warning a March decree banning genetically modified maize could also affect gene editing.