Study reveals how underwater volcanoes become explosive

Study reveals how underwater volcanoes become explosive. Most of the world’s active volcanoes are located underwater, where they are constantly reshaping the ocean. Recently, scientists discovered that submarine volcanic activity is not limited to the release of magma from vents and fissures, but is also capable of ejecting large amounts of volcanic ash.

An international team of experts theorized that there must be some underlying mechanisms that drive explosive eruptions in underwater volcanoes. 

“So even under layers of water kilometers thick, which exert great pressure and thus prevent effective degassing, there must be mechanisms that lead to an ‘explosive’ disintegration of magma,” said study co-author Professor Bernd Zimanowski of JMU Würzburg.

After analyzing the site of an underwater eruption that occurred in 2012, the researchers have produced the first report on what underlies explosive submarine volcanic activity.

The research was focused on the Havre Seamount volcano located northwest of New Zealand at a depth of about 1,000 meters below the sea surface. Here, an eruption in 2012 created a floating carpet of volcanic rock particles that expanded to about 400 square kilometers.

Observational data from a diving robot showed that more than 100 million cubic meters of volcanic ash was released during the eruption. The diving robot collected samples from the seafloor, which were then used in experimental studies. 

“We melted the material and brought it into contact with water under various conditions. Under certain conditions, explosive reactions occurred which led to the formation of artificial volcanic ash,” said Zimanowski. 

The team compared the artificial ash with real samples, and the results showed that processes in the lab must have been similar to natural reactions that took place on the seafloor.

“In the process, the molten material was placed under a layer of water in a crucible with a diameter of ten centimeters and then deformed with an intensity that can also be expected when magma emerges from the sea floor,” explained Zimanowski.

“Cracks are formed and water shoots abruptly into the vacuum created. The water then expands explosively. Finally, particles and water are ejected explosively. We lead them through an U-shaped tube into a water basin to simulate the cooling situation under water.”

The experimental particles corresponded in shape, size, and composition with natural ash particles.

“With these results, we now have a much better understanding of how explosive volcanic eruptions are possible under water,” said Zimanowski.

“With submarine lava eruptions, it takes a quite long time for the heat of the lava to be transferred to the water. In explosive eruptions, however, the magma is broken up into tiny particles. This may create heat pulses so strong that the thermal equilibrium currents in the oceans are disrupted locally or even globally.” 

Further research is needed to investigate whether underwater volcanic explosions have an effect on the climate.

The study is published in the journal Nature Geoscience.

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By Chrissy Sexton, Earth.com Staff Writer