Volcanoes/Mount Somma

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This apparent aerial or space image shows the small cone of Vesuvius sitting inside the much larger caldera of Somma. Credit: Don.

"Mount Vesuvius is a strato-volcano consisting of a volcanic cone (Gran Cono) that was built within a summit caldera (Mount Somma)."[1]

Somma-Vesuvius complex[edit]

"The Somma-Vesuvius complex has formed over the last 25,000 years by means of a sequence of eruptions of variable explosiveness, ranging from the quiet lava out pourings that characterized much of the latest activity (for example, from 1881 - 1899 and from 1926 to 1930) to the explosive Plinian eruptions, including the one that destroyed Pompeii and killed thousands of people in 79 AD."[1]

Theoretical Mount Somma[edit]

In the diagram, the cognoli of Somma are enumerated. Credit: Don.

In the diagram on the right, the lava flows from Vesuvius are indicated with black squiggly lines, whereas the lava flows of Somma are in green.

The gap between these two suggests the continued extent of the Somma caldera.

Entities[edit]

Mount Somma has a height of 1,132 meters at the Punta Nasone (the one in the middle of the mountain) and looks like a semi-circle in the shape of a truncated cone, in which Vesuvius is completely hidden. Credit: Don.

In the image above, Mount Somma has a height of 1,132 meters at the Punta Nasone (the high peak in the middle of the mountain) and looks like a semi-circle in the shape of a truncated cone, in which Vesuvius is completely hidden.[2]

On "the north side where it is well preserved, [as shown in the above image, Mount Somma] is characterized by a series of summits called COGNOLI. [...] Cognoli derives from the ancient verb "Scognolare", [for] "whet your teeth"! [The] Cognoli are the peaks of Monte Somma, [as] it looks in the picture, [each has] the typical shape of a tooth!"[2]

"Compared to the slopes of Vesuvius, which [are] more arid and sunny, the Monte Somma has a very humid environment, with an almost ... Apennine!"[2]

Tracing around the lush vegetation suggests that the original portions of Mount Somma are still present all the way around Vesuvius.

Mount Vesuvius[edit]

Vesuvius is shown from a plane. Credit: Pastorius.

Mt. Vesuvius is characterized as a "stratovolcano", or composite volcano, which means it is made up of pyroclastic material and lava. Vesuvius is the only volcano in the European mainland to have erupted within the last hundred years. Mount Vesuvius was known for its eruption in AD 79 and was named after the biologist Pliny. Since then, this volcano has erupted more than 50 times. Scientists have studied that this volcano is dormant. Its last eruption was in 1944, but is still capable of erupting. Mt. Vesuvius is located on the coast of the Bay of Naples about six miles from a short distance inland from the shore.

Geoseismology[edit]

Inferred 2D model of Somma obtained by tomographic inversion of first P-wave arrival times from shots S2, S3, and microearthquakes. Credit: A. Zollo, et al.

From geoseismology data an inferred 2D model of Mount Somma has been obtained in the image on the right.

"Solid circles indicate microearthquake locations."[1]

In the diagram on the right, the light blue, high velocity, thin layer northwest of S3 and below S2 to the southeast "correlates with the top of the Mesozoic carbonates, as detected from the Trecase well and gravity data."[1]

This light blue, large, high velocity region, its "location, shape, and P-wave velocities of this body indicate that it should have a magmatic origin, being either a high concentration of slowly cooled magmatic dikes or a part of the volcano that has suffered an intensive alteration by high- temperature hydrothermal fluids."[1]

"Our data do not provide any evidence for a molten magmatic body of more than 0.5 km in diameter down to 4 km of depth."[1]

"The occurrence of [...] mid-crustal high- to low-velocity discontinuities at depths of 10 to 20 km has been observed in several volcanic areas (19), where it is considered an indicator of large magmatic reservoirs."[1]

Hypotheses[edit]

  1. Changes in volcanic activity at the same location result from changes in the source of volcanism.

See also[edit]

References[edit]

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 A. Zollo, P. Gasparini, J. Virieux, H. le Meur, G. de Natale, G. Biella, E. Boschi, P. Capuano, R. de Franco, P. dell'Aversana, R. de Matteis, 1. Guerra, G. lannaccone, L. Mirabile, G. Vilardo (25 October 1996). "Seismic evidence for a low-velocity zone in the upper crust beneath Mount Vesuvius". Science 274: 592-4. http://people.na.infn.it/~zollo/articoli/SCIENCE_1996/zollo_et_al_science_1996.pdf. Retrieved 2015-03-18. 
  2. 2.0 2.1 2.2 Don (25 October 2014). "IZ8DPJ". QRZ.com. Retrieved 2015-03-18.

External links[edit]

{{Geology resources}}