Strong elevations and depressions are evident: Researchers have reconstructed the ground deformation in the Phlegraean Fields before, during and after the last eruption in 1538. Using models based on geological, archaeological and historical data, the dimensions of the deformations and the underlying processes become clear. The review could now shed light on current developments in the dangerous super volcano, say the researchers. At the moment, the Phlegraean Fields are causing renewed concern for volcanologists because of possible instabilities that could lead to an eruption.
A monster slumbers underground near the Italian city of Naples: The Phlegraean Fields (Campi Flegrei) are classified as a supervolcano because there is a huge magma chamber below and causes volcanic activity again and again. This became clear most drastically almost 40,000 years ago: A gigantic eruption shrouded half of Europe in ash and smoke and left a lasting mark on the region. The approximately 150 square kilometer area never really settled down after that. The last major eruption occurred in 1538: an eruption in the Phlegraean Fields created a new volcanic crater - the 132 meter high Monte Nuovo.
Does the monster wake up again?
An anxious look was directed towards the area again. For the past 70 years there has been a lot of rumbling: tens of thousands of small earthquakes have occurred and the coastal town of Pozzuoli has been lifted by almost four metres. A recent study concluded that these processes may have created critical instabilities that could lead to an eruption. This would have devastating consequences in the densely populated region. What exactly will happen now, however, remains questionable - because a renewed calm seems possible.
In the current study, the researchers led by Elisa Trasatti from the National Institute for Geophysics and Volcanology in Naples have now taken a look at the volcanic history of the region in order to be able to shed light on the present and the future. “Today, the ground deformations associated with volcanic activity are monitored both with satellites and with measuring networks installed on the ground. However, we still know very little about the behavior of volcanoes in the past, before the advent of the instrumental era," says Trasatti.
Researchers targeted the last major eruption in the Phlegraean Fields: the 1538 eruption that tore up Monte Nuovo. To reconstruct the sea level changes along the coast between 1515 and 1650, the team created a data set of geological, archaeological and historical data and used it as a basis for model calculations. "The application of mathematical models to simulate the Campi Flegrei magmatic system has allowed us to understand the behavior of the volcanic apparatus in the different phases of activity," says Trasatti.
Severe soil deformation
The data show that the eruption was preceded by a strong uplift of the ground, which initially affected the Pozzuoli area. Subsequently, the uplift was limited to the area of the future vent and reached a height of 20 meters, reports Trasatti. After the eruption, there was an alternation of subsidence and elevation, according to the models: "From 1538 to 1540, the caldera was initially affected by subsidence phenomena. From 1540 to 1582, i.e. for more than 40 years, the ground rose again before another phase of subsidence began, which lasted for a long time,” reports the researcher.
The models also provide indications of the underlying processes: "It becomes apparent that during the eruption a magma transfer took place between a source about four kilometers deep and the eruption vent of Monte Nuovo and that this phenomenon continued in the subsequent period, which was characterized by a Ground uplift was repeated due to the rise of new magma. However, since it did not reach the surface, this phenomenon has been dubbed an 'aborted eruption,'" says co-author Mauro Antonio Di Vito of the National Institute of Geophysics and Volcanology.
Another aspect concerns the estimates of the volume of magma: "It has been estimated that the amount of magma erupted in 1538 is only about one-hundredth of the amount that accumulated under the volcano between 1250 and 1650. This demonstrates the strong ability of the Phlegraean system to hold back the magma and erupt only a minimal part,” says co-author Valerio Acocella from the University of Rome Tre.
The conclusions based on the multifactorial data can now provide important information, emphasizes DiVito in conclusion. “Studying the past can help better understand current dynamics. Geological, stratigraphic, archaeological and historical data is an irreplaceable source of information that combines well with the data collected by the instruments used every day to monitor volcanoes,” says the scientist.
Source: National Institute of Geophysics and VolcanologyUniversity College London