A Tour of Italy's Fiery Trio
Rock&Gem Magazine|April 2020
A VOLCANIC FAMILY WITH COMPLEX PERSONALITIES
MARK LEATHERMAN
In May of 2019, my wife and I were able to enjoy our honeymoon, two weeks in Italy. It marked my first ever trip into Europe, and I could not skip the opportunity to accomplish another first, seeing my first stratovolcanoes up close and in person! After a great amount of convincing from my non-rockhounding new bride, we were able to book sightseeing time with Italy’s “big three,” Vesuvius, Etna, and Stromboli. Not only are these the only three active volcanoes in Europe, but they also have a very complex story to tell once one delves into their behavior and their constituent rocks.

MOUNT VESUVIUS

In starting our honeymoon in Venice, we proceeded to head southward with our final stop being the island of Sicily. After a memorable jaunt to Rome, our next stop was Naples, the primary base for visiting the historic town of Pompeii and the mountain responsible for its infamous sudden demise in 79 A.D. via a pyroclastic cloud.

We started our morning with an awe-inspiring tour of Pompeii’s ruins led by a graduate student of archaeology, Francesca, from the University of Naples. This cataclysm is primarily controlled by the fact that Vesuvius is classified as a composite volcano (a.k.a. stratovolcano). These volcano types occur at subduction zones, where a thin, but heavy oceanic plate subducts under a thicker, more buoyant continental plate. In this case, it is the African Plate subducting under the Eurasian Plate. Evaporating water from the down-going oceanic plate interacts and lowers the melting point of the mantle wedge above, creating magma that ascends to the surface.

Since said magma has incorporated the water vapor needed for melt generation, as well as other key elements and gases during its rise, eruptions associated with subduction are typically on the explosive side.

Although we had yet to ascend the mountain itself, we already experienced our first sampling of the variety of eruptive igneous rocks Vesuvius produced. Near the end of our tour, after viewing mostly structures made from marble, we were able to see some low-lying rooms and barriers made from a combination of yellow pumice and weathered tephrite. In general, Vesuvius erupts a myriad of rocks from across the igneous chemical spectrum. This includes felsic (light color-rich in silica, aluminum, sodium, and potassium), mafic (dark color-silica poor-rich in iron and magnesium), and those in-between (intermediate composition).

Composite volcanoes that are land-bound are known to produce eruptive rocks that are typically intermediate to felsic. The pumice is a lightweight felsic rock littered with gas-voids (where the yellow shades found here are a result of weathering). The tephrite is a type of intermediate rock composed of small and coarse crystals (the latter precipitating from underground magma, whereas the latter is cooled erupted lava that carried the larger pre-formed crystals to the surface). This is termed a porphyritic texture. Intermediate porphyry rocks are all but typical with stratovolcanoes, but these tephrites are a little different than their far-more common cousins, termed andesites. Tephrites differ in that they have no quartz, but a nominal presence of feldspathoid minerals (I call them “feldspar wannabes”), such as nepheline (Na, K)AlSiO4 and leucite (KAlSiO 3 ).

After enjoying a pizza lunch on the slopes of Vesuvius, our tour bus took us up to the parking trailhead, wherein we began a twenty-minute hike to the main crater. Along our ascent, the two dominant rock types we encountered were fresh blue-green tephrites and brick red scoria. After taking in the sights (and smells) of this inaugural visit to a stratovolcano crater, we enjoyed a short rolling-in of a wall of fog that obscured our panoramic view of Naples in the distance and made us feel like we had stepped foot on another planet!

MOUNT ETNA

After three days of relaxation along the AmalfiCoast, we took an overnight train to the famed island of Sicily to begin the last leg of our honeymoon. Although some sadness crept in, being near the end of the trip, I knew that the action was just about to heat up! We stayed in the town of Taormina and arranged a sunset tour of the southern portion of Etna. Once our guide, Giuseppe, collected four other tourists, we made our way through Catania; a town notably worn by time, nature, and economics.

The afternoon’s festivities began with a delightful stop serving as one benefit of Etna’s presence; a tasting of products made from the volcano’s fertile soil. Some of the delicacies sampled included: honey, wine, olives, and figs. After a half-hour of satisfying our palates, we continued upward the southern slope of Etna. With this volcano being the tallest in Europe, a drastic temperature change quickly set in from that of Catania, requiring us to bust out sweatshirts. Our first adventurous stop was to explore a small, recently-discovered lava cave right off the main road. While waiting for a prior tour group to wrap up their visit, I had some time to again explore some of Etna’s constituent rocks. While standing on black vesicular basalt flows, I noticed that we had parked right next to a raised mound composed of pahoehoe textures; a Hawaiianbased name used to refer to lava that cooled in a pattern resembling twisted ropes (or Laffy-Taffy).

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