References
Aveling, Ben. "Mt Etna, with Catania in the foreground." Wikipedia: The Free Encyclopedia. Wikimedia Foundation, Inc., 18 December 2007, https://commons.wikimedia.org/wiki/File:Mt_Etna_and_Catania1.jpg
Ubide, Teresa, and Balz S. Kamber. "Volcanic crystals as time capsules of eruption history." Nature communications 9.1 (2018): 326.
Many of
the world’s most populated areas are located near volcanoes, and that’s
unlikely to change. Volcanoes offer beautiful views, fertile soils, geothermal
energy, and other benefits that make it easy to understand why people are
attracted to living in these geologically hazardous regions. The island of
Sicily, Italy, has a population of over five million people who share their
island with Mount Etna (Figure 1), which is considered the most active volcano
in Europe. Mount Etna is a stratovolcano, a type of volcano known for having
highly explosive eruptions that can potentially result in pyroclastic flows,
which decimate anything in their pathway with hot ash and volcanic gases. They
are also known to produce lava flows, tephra falls, earthquakes, and even
tsunamis.
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| Figure 1: Mt Etna, with the city of Catania in the foreground, which has a population of over 300,000 people (Aveling, 2007). |
Since we
can’t directly observe what’s going on under the Earth’s surface,
volcanologists have to rely on clues to figure out when a volcano is going
to erupt. By observing the
characteristics of the rocks that were produced in previous eruptions, we can
identify how often a volcano tends to erupt and how the magma moves through the
volcano prior to an eruption. In this new research, Teresa Ubide and
Kamber Balz looked at clinopyroxene crystals to help understand the eruptive
history of Mount Etna.
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| Figure 2: Compositionally zoned clinopyroxene crystals. The arrows in the images are locations where the zones are high in chromium. Figure 2 from Ubide and Balz (2018). |
Clinopyroxene crystals offer a unique picture
of what happens beneath a volcano, because they grow at all depths of the
chamber and conduit. These
crystals tend to be zoned (Figure 2), meaning that they grow outward in
concentric rings, like the rings of a tree. Just as tree rings show seasonal
changes in the tree’s growth, crystal zones show how the crystals environment
changed as the crystal moved through the volcano. The changes in crystal chemistry were observed by using tools
to map the trace elements
from the centers to the edges.The researchers used their observations of the
crystals along with the temperature and pressure where the crystals grew to
help understand how magma moved under the volcano.
The research team used chromium to study the
volcano, because it occurs in high concentrations along with other elements
that are found in new magma (e.g. nickel and scandium). Because of this
association, when chromium suddenly becomes more common in a crystal’s zone, it
means that new magma has moved into the volcano. On the other hand, when a
crystal zone has less chromium it means
that the crystal was growing in magma that has spent more time in the magma
chamber. They also found that right before an eruption, the crystal grows a
chromium-poor rim, meaning that even if the eruption was triggered by new magma
moving into the system, it was not mixing with the crystals immediately prior
to their eruption.
The
research team looked at over 40 years of erupted clinopyroxene crystals from
Mount Etna. Using the growth rate of clinopyroxene, they found that almost all
of the crystals erupted within 2 weeks of a pulse of fresh magma into the
chamber. Magma entering the chamber pushes around rocks and magma that it
already there, creating swarms of small earthquakes. While not every pulse of
new magma will result in an eruption, scientists can now at least give better
warning of the high risk periods by watching for seismic events. While two
weeks may not seem like a lot of warning, it gives plenty of time to evacuate
at-risk populations. Mount Etna has increased in activity since the 1970’s and
so they hope that their findings can contribute a clearer picture for
scientists who work on mitigating volcanic hazards and help to protect the five
million people who live on the island of Sicily.
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