Osorno Volcano: Geologist warns of a rise in seismic activity and anticipates what a new eruption would be like

The most recent eruption of the Osorno volcano occurred almost 190 years ago. Despite this relatively long pause, The Osorno volcano has shown an increase in its seismic activity in recent years, reminding us how far it is from being a sleeping giant.

“The Osorno volcano used to erupt every 25 years, but since 1835 there have been no more eruptions. So since there is a historical record we have not had any event to know what the eruptions are like”, indicates Eduardo Morgado.

The volcanologist, academic of the School of Geology of the U. Mayor is the main author of first study that details the conditions that generated the last eruption of the Osorno volcano. The results of the research published in the Journal of Petrology They help to better understand the geophysical signals generated by the monitoring instruments about what happens on the surface of the volcano.

The investigation “is the one that gives us more detail of what happened before the eruption, what we lets you know what to expect in upcoming scenariosbecause the eruptions of the Osorno volcano of the last 12 thousand years have very similar characteristics, at least chemically, So we can expect that if a next eruption comes, it will be like the one in 1835, which was also similar to the last one. Villarica eruption of 1971explains the scientist.

Villarrica eruption of 1949. Photo: Chilean Memory

Osorno is a stratovolcano, which means that it is formed by multiple layers of lava that give it a perfect conical shape. It is located in the Los Lagos Region, 45 km from Puerto Varas. It has a maximum height of 2,661 meters above sea level and covers an area of ​​250 km2. Together with the La Picada, Puntiagudo and Cordón Cenizos volcanoes, it forms a chain of volcanoes that follows a line towards the Northeast.

The last eruption of the Osorno volcano in 1835 was observed by Charles Darwin. “…thin lines of incandescent lava shimmered on her sides, and the ship was shaken, as if the anchor chain were slipping.” noted the English naturalist in his travel notes aboard the scientific ship HMS Beagle under the command of Captain Robert Fitz Roy.

That eruption, Morgado points out, “It was not that violent from the point of view of the intensity, but it was partly a fissure eruption that broke part of the volcanic edifice through which magma came out, and it also had associated lahars”. Precisely It is these flows of sediment, rock and water that are generated by the eruption itself and slide along the slopes of the volcanoes, which represent the greatest threat to the Osorno volcano.

Eduardo Morgado, lead author of the study. Photo: U. Mayor

“The Osorno volcano is one of the most dangerous in Chile. The biggest danger is lahars, which have been registered; it is known where they have passed and which path they would follow if there were a new eruption and that is what should be paid more attention to”, warns the researcher.

The study further notes that the Recent activity of the Osorno volcano has shown an increase in its level of seismicity. “We are feeling many earthquakes associated with rock rupture, possibly because the volcano is releasing gases, but magma may also be coming from below,” Morgado says.

The volcanologist adds that “Other types of earthquakes have been felt that are generated by the movement of fluids.” These earthquakes are interpreted by geologists as signs of a phase of volcanic agitation indicating that the “system is still active and dynamic.”

The last explosion of the Osorno produced basaltic andesite and volcanic trepha, materials that contain minerals, whose chemical analysis allowed the scientific team of the U. Mayor know the parameters such as pressure, temperature, oxygen fugacity and amount of dissolved water from the magma prior to the most recent eruption on record.

Scientists taking samples. Photo: U. Mayor

The study combined several analytical techniques that were used to observe not only the chemistry of the minerals, but also the variations of the minerals and the glass. The work also involved comparisons of the eruption traces of other volcanoes in the area to understand the general context.

Eduardo Morgado details that “the minerals they store certain information and are rebalancing in the face of new conditions, but after erupting the temperature is so low that they are not able to rebalance and they keep those conditions that they had under the surface. What we do is, based on numerical modeling, try to find out that information that is recorded in the different phases”.

Numerical modeling of past eruptions is a recently applied method to study volcanoes in Chile. It has only been used since 2017 to help “the best interpretation of geophysical, satellite, seismology, inclinometer, GPS signals, which are indirect signals that are complemented by the information on the magma that we study, which is direct,” explains Morgado. .

Could the Osorno volcano surprise us with a new eruption? “Yes”, answers the academic, who then specifies that such an event could probably take another 50 years. Volcanoes “are chaotic systems and very difficult to predict, the important thing is to be attentive,” he concludes.