Russian and Colombian scientists are monitoring the breathing of the Nevado del Ruiz volcano in Colombia. Geophysicists have developed an algorithm that makes it possible to estimate periodic changes inside the volcano with the help of earthquake data.
The results of the study are published in the prestigious journal. Scientific Reports by the Nature group. Ivan Koulakov , co-author of the article, head of the Laboratory of Seismic Earth Imaging at NSU and the Laboratory of Seismic Tomography of Trofimuk Institute of Petroleum Geology and Geophysics, SB RAS, corresponding member of the RAS talked about this work.
Nevado del Ruiz
— The Nevado del Ruiz is one of the most dangerous volcanoes in the world with an altitude of 5,321 m. In 1985, hot lava and gasses were released to the surface as a result of a moderate eruption. Consequently, lava and gasses melted the ice cover on top of the volcano. A hot flow of mud and stones (also called lahar) rushed down the densely populated valley reaching the town of Armero, located 30 km from the volcano. The lahar almost entirely buried the inhabitants of Armero and killed more than 25 thousand people, says Ivan Koulakov.
Scientists admit that today, in the case of a larger eruption, which is considered very likely to happen with this volcano, an area with a population of about half a million people may be at risk.
Since the catastrophe in 1985, Colombian authorities have made significant efforts to establish modern monitoring systems that can quickly detect signs of volcanic danger. As a result, Nevado del Ruiz now has one of the best seismic networks in the world among active volcanoes.
Co-authors of the article: Ivan Koulakov and Carlos A. Vargos on the Nevado del Ruiz volcano at an altitude of 4500 meters. The area behind the fence is considered as dangerous, because it is too close to the volcano
In 2011, after a lull of several decades, Nevado del Ruiz resumed its activity. The volcano emits a lot of gasses into the atmosphere. The output of sulfur dioxide (SO2) from the crater amounts to 2 million tons per year; on some days the mass of this gas reaches 30,000 tons. Furthermore, a lot of small-scale earthquakes occur daily beneath the volcano. Although these earthquakes are not felt by local inhabitants, they are constantly being registered by the instruments by the seismic network and indicate the activation of the plumbing system.
Ivan Koulakov visited Colombia in August 2016. He asked Colombian geophysicists for permission to use their long-term data on earthquakes in his work and they agreed. Together with a fourth-year student in the geological-geophysical faculty at NSU — Valery Gladkov, he developed an algorithm that reveals changes in the seismic structure beneath the volcano over time.
—These earthquakes act like light bulbs that illuminate the insides of the planet for us. Seismic rays from these light bulbs carry information about the structure of the Earth. Our task is to decipher this information, says the scientist.
At the foot of the volcano
Based on a large amount of seismic data, the tomographic inversion has revealed a seismic anomaly beneath the Nevado del Ruiz volcano at a depth of 2-4 km. Over a period of ten years its shape and size have revealed significant changes.
— This anomaly is a reflection of complex processes occurring inside the volcano. It is related to the presence of a liquid phase (melts or fluids) in a magma chamber — a reservoir in a Colombian volcano. In 2010, the intensity of the anomaly was at its height, which indicates maximum fluid saturation in the magma chamber beneath Nevado del Ruiz. In such cases, there is always a risk that the transition of liquid fluids into a gas phase will go avalanche-like and lead to an explosion. Fortunately, in this case, the eruption had a different scenario. In 2011, a gradual bleeding of gasses began through a hole in the crater and, probably, through cracks in the uppermost crust. Since that time and until 2014, the seismic anomaly has gotten smaller and virtually disappeared. The reservoir of the volcano became empty and the magma, that remained in it, started to crystallize, says Ivan Koulakov.
One could have assumed that this marked the end. However, in 2015 results showed that the cringed anomaly began to increase again. The volcano started to gain «liquid».
Change in seismic anomaly over time. Photo by Scientific Reports
— This process can be compared with breathing: inhale-exhale. Judging from our data, the camera directly below the volcano is part of a multi-level system consisting of several reservoirs connected to each other. Reducing the pressure in the upper reservoir, as a result of the release of gasses into the atmosphere leads to the «absorption» of the liquid fraction from another deeper reservoir. However, part of the upper reservoir is already filled with a crystallizing magma. Under the influence of excessive pressure, a highly viscous magma is being squeezed out of the cone of the volcano like toothpaste from a tube.
According to the scientist, many factors indicate, that the Nevado del Ruiz volcano is taking a breath again.
Scientists are aware of many signs of an awakening volcano. In 2010, Colombians, acting independently of Russian geophysicists studies, understood the full danger of the situation. However, the primary challenge is always to predict the nature of the future eruption. Will it be calm or explosive?
— Our work can be used as current monitoring. It allows us to observe the periodic change in seismic properties of the magma reservoir, associated with the process of Nevado del Ruiz «breathing». This kind of work will allow us to identify the most dangerous periods when the volcano's «lungs» are full and ready for a quick release. It is still premature to talk about the concrete implementation of our development in terms of an everyday application. But, we will most likely get to this in the near future.