Tiny Volcano Crystals Could Help Predict Eruptions

Predicting when a volcano will explode can be a very difficult task. Each volcano has its own unique and complex maze of tunnels that carry magma to the surface. So even if we detect volcanic activity, it’s difficult to know when magma will pass through these tunnels and erupt.

But there is now a way to assess this process using crystals that grow inside volcanoes, just as there is a record of eruptions. Our latest study of crystals from Italy’s Mount Etna shows that if new magma reaches the chambers 10 kilometres below the surface of Mount Etna, an eruption can occur within two weeks. No wonder the Roman poet Lucretius said that Etna volcano “bursts into flames from the lowest recesses of hell.”

Geologists once thought that the magma under volcanoes was in a large single chamber, but modern research shows that feed systems contain many connected compartments with complex transport routes. We also know that when new magma energizes these volcanic feed systems, it triggers an eruption.

As the magma moves toward the surface, the newly stirred magma pushes the rock away from the volcano, creating pressure underneath the volcano. This creates earthquakes and expands the volcano’s cone-shaped edifice, and these effects can be monitored at the surface or from space with satellites. The difficulty is knowing whether a particular magma supply will actually translate into an eruption, and how long it will take to start erupting.

This is where crystals can come into play. These minerals are called ant crystals (“ant” means before) because they usually start growing from early magma thousands of years before a volcano erupts. They grow layer by layer, recording changes in the magma around them, just as tree rings record changes in climate.

Laser technology now means we can look at anticrystals to create maps of the trace chemical elements within them. This mainly involves emitting a grid of laser lines at the anticrystals and then using what is known as a mass spectrometer to analyse the emitted aerosol and calculate the elements it contains.

This can be used to create a two-dimensional image of the crystal’s composition, which tells us something about its history. For example, when an ancient pre-crystalline nucleus is transported to the surface by newly stirred magma, it creates a distinctive edge on the crystal. Our challenge is to extract meaning from these records.

Mapping Etna
Using a crystal chemistry map of volcanic activity at Mount Etna over the past 40 years, we have been able to determine the depth of crystal growth, as well as when new magma began to intrude into the underground volcanic system. We have found that this began to occur in the 1970s, coinciding with the volcano beginning to erupt more frequently, with faster flowing magma and greater explosive and seismic activity.

The type of contact between the core and rim of the crystals and the thickness of the rim hold information on how much time passed between the magma batch and the start of the eruption. This means that we can better predict when an eruption might occur after magma is detected at certain points beneath the volcano (in this case, two weeks after reaching depth).

In this way, laser surveys of anticlasts around the world can help volcanologists better understand how magma supply acts as a trigger for eruptions and how to interpret monitoring data from active volcanoes. This could create a more accurate process for spotting warning signs and predicting impending eruptions.