Paroxysmal initial phase.
The term paroxysm actually comes from the medical field and describes a special type of spasm. In volcanology, " spasmodic" volcanic eruptions are called paroxysms, in which the eruption slowly increases, only to end in a strong eruption, whose peak phase lasts only a short time and ends very quickly. One can distinguish 3 phases:
How a paroxysm occurs is not yet 100 percent understood. The volcanologist Dr. Boris Behncke of the INGV assumes that the formation of bubbles in the magma chamber and conveyor system is of particular importance. Under certain conditions a kind of foam develops from magma and water vapour bubbles. When this foam decompresses, it bubbles up like a shaken champagne bottle with the cork popping and foamy champagne bubbling out. More and more gas bubbles form and drive the magma out of the vent, increasing the eruption to a lava fountain.
Tectonics of the Etna regionThis type of eruption is typical for Etna in Sicily. Here, impressive phases of paroxysmal volcanic eruptions between 1999 and 2001 have been observed. The scene was mainly the southeast crater. However, paroxysms from Bocca Nuova occurred in October 2000. The Southeast Crater produced 77 of these eruptions during this period. The eruption series culminated in the flank eruption in July 2001.
In October-November 2006 a smaller series of paroxysms occurred. This ended with the opening of a fracture on the southeast flank of the southeast crater cone. Several lava flows were produced before the eruption. A hornito formed at the edge of Valle de Bove and was strombolian active for several days. In January 2011, another series began, the scene of which shifted from the southeast crater further to the east. There the cone of the "New South East Crater" was formed from a pit crater. Until April 2012, 19 paroxysms occurred. From April 2012 to 20 February 2013, no such eruptions occurred on Etna. Then the calm ended and until the end of April there were 13 of these eruptions.
The beginning of the peak phase of a paroxysm is often marked by the outflow of a lava flow. From then on it often takes only minutes until a continuous lava fountain develops from strombolian eruptions. This can reach a height of up to 1000 meters and the plateau in front of the crater cone turns into an inferno of red-hot lava bombs that hit close together. Those who are then still close to the crater have bad cards. Depending on the wind direction, lava bombs can still hit at a distance of 2-3 kilometers.
While the lava flows mostly flow into the Valle del Bove and do not cause any further damage, the tephra from the eruption cloud can come down many kilometers away and strongly affect public life. Especially affected are the villages in the eastern part of Etna, down to the coast. Lapilli cover streets, cars and roofs, which have to be cleared at great expense. The fine dust pollution is exorbitantly high. Nevertheless it is a very special experience to observe a paroxysm. Such a natural spectacle is rarely offered.