Dome-building volcanoes, which are frequently active, are among the most dangerous types of volcanoes, as they are known for their explosive activity. This type of volcano often erupts first silently producing a dome-shaped extrusion of thick lava at its top that is too viscous to flow. When it finally destabilizes, it ruptures and produces rapid streams of hot gas, chunks of solidified lava, and volcanic ash, called pyroclastic clouds, that flow down the sides of the volcano at the speed of a fast train. “The hazards associated with them can be very spontaneous and difficult to predict,” said Professor Thomas Walter, professor of volcanology and geological hazards at the University of Potsdam in Germany. “That is why it is so important to understand this phenomenon of lava domes.”
Little is known about the behavior of lava domes, in part because not much data is available . Professor Walter and his colleagues want to better understand how they are formed, if they can vary significantly in shape and what their internal structure is like. For the past five years, through a project called VOLCAPSE, they have been using innovative techniques to monitor lava domes using high resolution radar data captured by satellites, as well as close-up views from cameras installed near volcanoes. “Pixel by pixel, we were able to determine how the shape, morphology and structure of these lava domes changed,” said Professor Walter. “We compared (the webcam images) to the satellite radar observations.”
Lapse of time
The project focused on some dome construction volcanoes such as Colima in Mexico, Monte Merapi in Indonesia, Bezymianny in Russia and Monte Lascar and Lastarria in Chile. In part, it involved visiting them and installing instruments like solar panel-powered time-lapse cameras that could be controlled remotely. If a lava dome began to form, for example, the team could modify the settings to capture higher-resolution images more frequently. Due to the high altitudes and harsh weather conditions, setting up the cameras was more challenging than expected. “It was a sharp learning curve, but also trial and error, because no one could tell us what to expect at these volcanoes, as it had never been done before,” said Professor Walter.
During their visits, the team also used drones. These would fly over a lava dome and capture high-resolution images from different perspectives, which could be used to create detailed 3D models. The drones’ gas and temperature sensors provided additional information. Professor Walter and his colleagues used the data to create computer simulations, such as how the growth of lava domes changes from one eruption to another. They found that new lava domes do not always form in the same place: a lava dome can form on top of a volcano during an eruption, while the next time it accumulates on one of its flanks. The team was puzzled, as a conduit inside a volcano brings magma to the surface during an eruption, which would mean that it changes its orientation between one eruption and the next. “That was very surprising to us,” said Professor Walter.
Stress field
They were able to explain how this happens by examining the distribution of internal forces, or the stress field, in a volcano. When magma is expelled during an eruption, it changes the way forces are distributed within, causing a reorientation of the conduit. The team also found that there was a systematic pattern to how the stress field changed, meaning that by studying the position of the lava domes, they could estimate where they had formed in the past and where they would appear in the future . This could help determine which areas near a volcano are likely to be most affected by eruptions to come.
“This is a very good result for predictive research if you want to understand where the lava dome will come from (or collapse) in the future,” he said.
Knowing where a volcano will erupt from is one thing, but knowing when it will erupt is another matter, and the physical factors that govern this are also not well understood. Although there is a relationship between the frequency with which eruptions occur and their size, with large eruptions occurring very rarely compared to smaller ones, the lack of reliable data makes it difficult to examine the processes that control the frequency and magnitude of eruptions. eruptions. “When you go back to the geological record, (traces of) many eruptions disappear due to erosion,” said Professor Luca Caricchi, professor of petrology and volcanology at the University of Geneva in Switzerland.
Furthermore, it is not possible to access these processes directly as they occur deep within a volcano, at depths of 5 to 60 kilometers. Measuring the chemistry and textures of the magma ejected during an eruption can provide some clues about the internal processes that led to the event. And magma chambers can sometimes be investigated when they arise on the Earth’s surface due to tectonic processes. However, extracting information from specific time periods is still difficult, as the “picture” you get is like a movie in which all the frames are collapsed in one shot. “It is difficult to recover the evolution in time, what really happened during the film,” said Professor Caricchi.
Professor Caricchi and his colleagues are using a novel approach to forecast the recurrence rate of eruptions. Previous predictions were typically based on statistical analysis of the geological records of a volcano. But through a project called FEVER, the team aims to combine this method with physical modeling of the processes responsible for the frequency and size of eruptions. A similar approach has been used to estimate when earthquakes and floods will occur again.
The use of physical models should be especially useful for making volcano predictions where little data is available. “To extrapolate our findings from a place where we know a lot, like Japan, you need a physical model to tell you why the frequency-magnitude relationship changes,” said Professor Caricchi. To create their model, the team incorporated variables that affect the pressure in the magma reservoir or the rate of magma accumulation deep below the volcano. The viscosity of the crust under the volcano and the size of the magma deposit, for example, play a key role. They have run over a million simulations using all possible combinations of values that can occur. The relationship between frequency and magnitude that they obtained from their model was similar to what was estimated using volcanic records, so they believe they were able to capture the fundamental processes involved.
“It is a kind of struggle between the amount of magma and the properties of the crust”, clarifies Caricchi. “They are the two great players fighting each other to finally bring this relationship.”
Tectonic plates
However, the team also found that the relationship between the size and frequency of volcanoes changes in different regions. Professor Caricchi believes this is due to the differences in the geometry of the tectonic plates in each area. “We can see that the speed at which one plate subducts under another, and also the angle of subduction, appears to play an important role in defining the frequency and magnitude of a resulting eruption,” he said. The team is now beginning to incorporate this new information into their model.
Being able to predict the frequency and magnitude of future eruptions using a model could help better assess hazards. In Japan, for example, one of the countries with the most active volcanoes, knowing the probability of future eruptions of various sizes is important when deciding where to build infrastructure such as nuclear power plants.
It is also invaluable in densely populated areas, such as Mexico City, which is surrounded by active volcanoes, including Nevado de Toluca. Professor Caricchi and his colleagues studied this volcano, which has not erupted for about 3,000 years. They found that once magmatic activity restarts, it would take about 10 years before a major eruption could occur. This knowledge would prevent the evacuation of Mexico City if initial signs of activity are detected. “Once the activity restarts, you know that you have ten years to follow the evolution of the situation,” said Professor Caricchi.
Original article
This article was originally published in Horizon, the EU Research and Innovation Magazine
