Rome’s volcano is slowly stirring

The Alban hills sit some 30km outside Rome, and much of the tuff (consolidated volcanic ash) used to build in the Eternal City was quarried here in this volcanic field (an area with lots of small eruptions of varied types spread over time rather than a repeatedly built up and exploded cone shaped peak and crater system) out of the remnants of a series of eruptions that ended some 36,000 years ago. The most intense eruptive phase included a caldera forming event that left behind a 10x12km crater where a chunk of the surface dropped into the newly emptied magma chamber below sometime between 600,000 and 350,000 years ago, though activity has been calmer since.

While long though extinct, new research suggests that the system is in fact still active, and the magma chamber below slowly refilling some 5-6km down, though any eruption is thought to be a good millennium or two away. A swarm of minor earthquakes in the 1990’s was the first symptom, followed by the formation of a steam vent, where circulating cells of convecting groundwater are heated by contact with magma heated rock and flash into steam when they reach lower pressures close to the surface. Another appeared by one of Rome’s airports in 2013. Now the hills are slowly inflating, to the tune of some 2mm every year amounting to half a metre in 65 years. The team suggest that a fracture opened in the deep crust below some 2,000 years back, and as batches of magma gradually rise through the system it has grown to the point where an appreciable quantity of molten rock is making its way through.

When it does eventually come, historical evidence suggests that it will be explosive, likely to spew large quantities of blasted finely powdered ash over the immediate area, though the intensity has been diminishing with each series. Many volcanoes thought extinct (including, once upon a time Mt St Helens) are in fact dormant, and dating the successive layers of ash and fossilised soils between them suggests that in some cases many tens or hundreds of thousands of years can pass by between eruptions. Here it has varied between 29 and 57,000 years since the main event. The team hope the slow development of this volcanic system will prove a good testing ground for monitoring technology and practices that can then be applied elsewhere to more dangerous volcanoes such as Vesuvius and Campo Phlegrei that threaten some 3 million people in and around Naples.

Loz

Image credit: 1: Renato Clementi 2: Deblu68

Original paper, free access: http://bit.ly/29TaKNYhttp://bit.ly/29Pt4IZhttp://bit.ly/29PShkkhttp://bit.ly/2aaAFBNhttp://bit.ly/29PShkkhttp://bit.ly/29SIs5V