‘Cataclysmic Italy’ talk fascinated Crediton U3A members

By Crediton Courier Contributor   |   Crediton Courier Contributor   |
Saturday 6th August 2022 11:00 am
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FOLLOWING information and notices on July 20, Crediton and District U3A members experienced a surprise item.

The Ukulele Band, one of the groups on offer at u3a, gave us a rendition of “Da Doo Ron Ron”.

The band is open to all paid-up members; you don’t have to be able to play well, just be enthusiastic. We then had our regular monthly talk, this time a talk entitled “Cataclysmic Italy” by Professor Peter Edwards.

Professor Edwards gave us an excellent talk explaining why Italy was so affected by volcanoes and earthquakes.

It’s a consequence of earth’s solid surface (crust) being divided up into sections called tectonic plates.

These are “floating” on a semi-molten layer of rock called the mantle. The mantle is constantly moving, dragging the plates on top with it.

Professor Edwards compared the mantle’s movement to the convection currents in a lava lamp, but you can also see convection currents if you look at the air above a hot radiator.

In some places hot, less dense mantle is rising like the hot air above a radiator.

An example of this is the Mid-Atlantic ridge. New rock comes to the surface, pushing the American tectonic plates away from the European and African tectonic plates at the rate of about 2cm a year.

In other places cooler, denser mantle is sinking. This brings two tectonic plates closer together.

Sometimes the plates collide and pile up to form mountains. The Himalayas are an example of this. In other places, one plate slides under another. This is called a subduction zone.

The plates do not slide smoothly, and it’s this juddering we feel as earthquakes. As the surface material of rock and water gets pulled under, the rock starts to melt and, when mixed with very hot steam, rises to the surface to form explosive volcanoes.

The eastern side of Italy lies on a subduction zone between the Eurasian plate and the African plate.

In fact, the Po valley of Italy is part of the African plate that protrudes up the Adriatic Sea.

As the African plate slides under Italy, we get earthquakes in a line running north-south down the centre of Italy.

Professor Edwards showed us some very moving pictures taken of earthquakes in Italy during the last 100 years.

Earthquakes are measured using the Richter scale. This scale can be a bit confusing as it is a logarithmic scale.

An earthquake of 6 is 10x stronger than an earthquake of 5. Earthquakes of 5 or more will cause damage to some buildings, but earthquakes of 6 or more can be disastrous.

Italy has had more than 11 big earthquakes in the last 100 years and many, many smaller ones.

In 1997 Umbria experienced an earthquake of 6.4. We were shown a video that was taken by chance by some scientists filming inside the church of St Assisi at the time of the earthquake. The inner ceiling of the church fell in and sadly some people were killed.

Severe damage was done to the structure of the church including the ancient and irreplaceable frescoes. Although now restored, a crack remains down the centre of one fresco.

Running down the west side of Italy there is a chain of 30 volcanoes: some live, some dormant and some extinct. These are where molten rock and steam from the mantle is once again rising to the surface.

There are three live volcanoes: Etna, Stromboli and Vesuvius. Vesuvius erupted as recently as 1944, but Stromboli and Etna are both also very active. There are also other active areas, for example Solfatara di Pozzuoli, the only privately owned dormant volcano. This is a shallow crater near Naples which emits clouds of sulphurous steam.

Professor Edwards asked: “Should you be put off visiting Italy by this tale of woe?”

Probably not. There are many places in the world that experience similar geological activity. However, you might think twice before buying a house there.

• Exploring Our Fluid Earth is based on the nationally recognised Fluid Earth/Living Ocean (FELO) aquatic science curriculum (Klemm et al., 1990; Klemm et al., 1995)

Sandra Ragalsky

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