For those of us who track volcanoes and the hazards they present, the general consensus is that Mount Vesuvius in Italy is probably the most dangerous volcano in the world today. This is not because it is the biggest or most powerful, but because it is located on the outskirts of Naples, Italy, a city with over 2 million inhabitants (including the surrounding area). Evacuating such an area quickly and efficiently during a time of crisis might be, well, impossible. We know that Vesuvius can be destructive - just look at the fact that much of the Naples area is built on the deposits of the volcano that has repeated buried the area (and former cities like Pompeii and Herculaneum) - and we know it is a vigorously active volcano, with its last eruption only ~60 years ago. Naples is a powder keg for potential volcanic destruction, and it is just waiting for the spark that Vesuvius might provide.
However, with all that being said, there have been a flurry of recent reports downplaying the potential destructive future behavior at Vesuvius. The long and short of this research conducted by Michel Pichavant and Bruno Scaillet from the University of Orleans (France) is that the magma chamber at Vesuvius is getting shallower (closer to the surface) over the last few thousand years. Their findings (although never explained in the articles is how they came to these findings, a big peeve of mine) suggest that the magma chamber that produced the lavas that have erupted in the last few hundred years (my italics) has risen from ~5 km depth to ~2.5 km depth. This might suggest that future eruptions if from this chamber (my italics) might be less explosive as magma stored at shallower depths to degas easier (less confining pressure), thus preventing catastrophic degassing that produces explosive eruptions - think of the different between opening a bottle of fresh soda (deep chamber) versus flat soda (shallow chamber). These data are interesting, however, they only suggest that the recently tapped magma chamber is shallower. It does not offer any insight to whether future eruptions might originate from deeper in the system if there is a new influx of magma from depth. If that is the case, all bets are off in terms of the lower perceived danger of Vesuvius.
Comments (109)
Dear Erik, it's nice to read you.
About Vesuvius and the upper magma chamber I have an idea. Tomographic surveys show the occurence of a magma chamber some 8 kilometers deep and don't show a similar structure upwards.
So I was surprised when I have read this hypotesis.
So, appartently, the geophisial data desagree the petrological ones. But there is a solution, wich also can explain the loop beetwen active and non-active stages: a strong event (as in 79 AD) is accompanied by a magma uprise, wich remains at a lesser deep. So, in periods when hot magma is in higher position, there is magmatic activity, wih is absent when the upper magma chamber is too much cold or has no more magma reservoir.
An eruption as the pompeian one drives magma in the upper chamber, and so the activity turn on, somehow as a consequence of the plinian eruption.
This could be a solution, but if so we must explain how a magma chamber could delivery molten materials 60 years ago and now is completely vanished, as the tomography says.....
Posted by: aldo | September 20, 2008 6:30 PM