Volcanoes are known for their explosive power and destructive force, but scientists still have much to learn about the processes behind eruptions. A new study conducted by researchers from Imperial College London and several international institutions sheds light on the unexpected routes magma takes beneath volcanoes, revealing key information about the type and rate of volcanic eruptions, as well as the make-up of erupted magma.
When two tectonic plates collide, one plate subducts beneath the other and plunges into Earth’s mantle, releasing water and melt. These subduction zones are responsible for some of the most hazardous earthquakes and explosive volcanic eruptions. However, it has been difficult to understand exactly how magma forms underground and what controls the position of volcanoes.
Now, this new study published in Science Advances shows that rising magma, which eventually erupts, does not always take the shortest, most direct path to reach volcanoes. Lead author Dr. Stephen Hicks explains that the interplay of two driving forces – the subducting plate and the overlying plate – over hundreds of millions of years is key to determining where eruptions occur.
Subducting oceanic plates act as reservoirs for water and other volatile elements, which are driven off by the high pressures and temperatures of the subduction process. These fluids and melt eventually become the key ingredients of magma that erupts from volcanoes. However, the pathways that these elements take from the subducting plate to the volcanic arc have been difficult to infer.
To carry out the study, the researchers used earthquake data to map seismic absorption in 3D, using ocean-bottom seismometers to build an accurate picture of the subsurface. The results showed that the strongest seismic attenuation was offset from beneath the volcanoes, leading the authors to conclude that once water is expelled from the subducting plate, it is carried further downwards and causes mantle melting behind the volcanic front.
Study co-author Professor Saskia Goes notes that the researchers focused on the subduction of the Atlantic rather than the Pacific, as the oceanic plate in the Atlantic was formed more slowly and subducts more slowly, making the fluid and melt pathways more visible using seismic waves.
„Our findings give us important clues about the processes behind volcanic eruptions, and could help us to better understand where the magma reservoirs below volcanoes get formed and replenished,” said Goes.
A Journey Through the Mantle
The results of this study offer a unique perspective on the complex journey of magma beneath volcanoes. By mapping the seismic absorption of earthquakes, the researchers were able to shed light on the unexpected routes magma takes and the key processes behind volcanic eruptions. With further research, these findings could help us understand why some volcanoes are more active than others and why volcanic activity changes over time.
So the next time you see a volcano erupting, you can imagine the journey the magma took to reach the surface, and the many geological processes that were involved in shaping its path.