Crystals can help predict volcanic eruptions

Imagine having a crystal ball that could predict the next volcanic eruption. For millions of people living near active volcanoes, such a tool would be invaluable. 

Interestingly, some crystals formed deep within the Earth can indeed help forecast volcanic activity. These crystals, which are created as molten rock travels from beneath the Earth’s surface, hold vital clues about past eruptions.

Crystals hold a record of eruptions 

By employing advanced scientific methods, researchers can extract a hidden record from these crystals, uncovering the reasons, locations, and timings of previous eruptions. This historical information can help interpret early signs of volcanic unrest, such as earthquakes, which often signal magma moving toward the surface. 

In a new column in Nature Geoscience, Teresa Ubide, a geoscientist at the University of Queensland, discusses how we are getting closer to having crystal balls – at least for volcanoes.

Crystals formed by cooling magma

When magma, the extremely hot molten rock that powers eruptions, forms tens of kilometers below Earth’s surface in the mantle, it begins a complex journey upward. 

During this trip, magma may pause in reservoirs and travel through a winding path before eventually erupting. As magma ascends, it cools, forming small crystals that can be carried to the surface during eruptions.

Once magma reaches the surface, it can either flow as lava or explode into fragmented particles known as pyroclasts. As these materials cool, they solidify into volcanic rocks, which preserve the crystals formed deep within the Earth. These crystals serve as “crystal balls,” preserving the memory of everything they experienced inside the volcano.

Distinct appearance of volcanic crystals

The appearance of these crystals depends on their mineral composition. For instance, the green olivine found in Hawaiian lavas and the white plagioclase crystals in the Tweed volcano’s lavas on the Queensland-New South Wales border are distinct examples. 

However, one of the most critical minerals for studying volcanoes is clinopyroxene. This mineral produces shiny black crystals that hold essential information about the inner workings of volcanoes.

Chemical changes within the crystals 

Clinopyroxene crystals may be as tiny as a grain of sand, but under a microscope, they reveal extraordinary details about volcanic activity. They grow in concentric zones, similar to tree rings, with each zone documenting changes in the magma environment within the volcano. 

The outermost growth zone is particularly important, as it can indicate if an eruption was triggered by fresh magma rising from deep within the Earth. 

By analyzing the chemical changes within these crystals, scientists can estimate how long it took for magma to reach the surface – information that could help predict future eruptions.

Indications of potential volcanic eruptions

These crystals sometimes grow with different compositions in various directions, a phenomenon called sector zoning, which resembles an hourglass inside the crystal. 

Sector zoning provides further clues, suggesting that the magma underwent complex processes such as mixing with other magma, releasing gas, or rising quickly before an eruption. 

By identifying these processes in the crystals, volcanologists can watch for similar signs at the surface, offering early indications of potential volcanic activity.

It’s also critical to identify where within the volcano these eruption triggers occur. This information can help determine if certain depths, where earthquakes or ground deformations occur, are particularly significant for predicting an eruption.

Pressure conditions during crystal formation 

The chemical makeup of clinopyroxene crystals also provides clues about the pressure conditions during their formation, which can be translated into the depth of magma storage below the surface. 

Analyzing these chemical variations requires cutting-edge laboratory techniques, such as using lasers the width of a human hair or focusing intense synchrotron light from particle accelerators like the one in Melbourne, Australia. 

These tools enable scientists to extract detailed information about the magma’s journey from the microscopic structures of the crystals.

Next time you hike near a volcano, whether it’s in Hawai’i, Iceland, or the Glass House Mountains in Australia, look closely at the rocks for colorful specks. These tiny crystals are the keys to unlocking the history of the volcano – and they might also offer insights into its future.

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