Long-dormant volcanoes can erupt quickly and explosively, Ciomadul study finds

Can a volcano erupt after tens of thousands of years of dormancy? If so, how can this be explained and what makes volcanic eruptions more dangerous?

These are key questions in volcanic hazard assessment and can also draw attention to volcanoes that appear inactive. Even in a calm, dormant phase, a volcano can quickly become active and its eruption can pose a previously unknown threat to the surrounding region. New research by Hungarian scientists helps reveal the signs before such a volcano erupts.

A team from ELTE Eötvös Loránd University, the Institute of Geography and Earth Sciences, and the volcanology research group HUN-REN-ELTE, in cooperation with other European scientists, studied Ciomadul, the youngest volcano in the Carpathian-Pannonia region.

Using integrated high-resolution data on mineral texture and chemical composition, they quantified the conditions of magma evolution, reconstructed the architecture of the subvolcanic magma reservoir, identified the characteristics of the resident crystal mush and recharge magmas, which triggered the eruptions, and explained why. volcanic activity during the last active period became primarily explosive.

Ciomadul: a typical volcano that has been dormant for a long time

The eruptive history of Ciomadul was previously revealed by the research team using the U-Th-Pb-He geochronology of a tiny crystal, zircon. Szabolcs Harangi, professor and leader of the research project, says that “there have been several long periods of dormancy during the life of the volcano, which spans almost a million years, but even after tens of thousands, sometimes even more than 100,000 years of tranquility, volcanism and eruptions have started again. »

The most significant volcanism has occurred in the last 160,000 years, with extrusions of lava domes between 160 and 95,000 years ago, then, after more than 30,000 years of dormancy, eruptions resumed there is 56,000 years old.

Barbara Cserép, Ph.D. student at ELTE, studies the youngest eruption products. “They were formed by explosive eruptions that were more dangerous than the previous active episode. So it is important to know what was the reason for this change in eruption style,” she says. The last volcanic eruptions took place 30,000 years ago and since then the volcano has been dormant again.

Petroleum detective work

The cause of the triggering of the volcanic eruption and the processes that control the style of the eruption are hidden in the rocks formed during volcanic activity. These can be revealed by the detailed study of the minerals forming the rock. The research team determined the chemical composition of all mineral phases, often at high resolution, from the crystal core to the edge, in pumice stones formed during explosive volcanism 56 to 30,000 years ago.

They then critically evaluated the results of various methods for calculating crystallization temperature, pressure, redox state, melt composition, and melt water content to quantify the conditions magma and also to limit the way in which these crystals were incorporated into the erupting magma. This helped unravel the architecture of the magma reservoir system, the processes that lead to eruptions, and explain explosive eruptions.

The key to explosive breakouts

The key player in this petrodetective study was a mineral called amphibole. “Many elements can fit into the amphibole crystal lattice, but element substitutions are strongly controlled by magmatic conditions,” explains Barbara Cserép.

The chemical composition of amphibole in Ciomadul pumice stones shows wide variation even in a single sample. Some amphiboles represent a reservoir of highly crystalline, low-temperature magma at depths of 8 to 12 kilometers, but most of them were transported to this shallow magma storage by higher-temperature recharge magmas from greater depths.

“Compared to the previous eruptive period, forming lava domes, these fresh recharge magmas carried amphiboles with a distinct composition, that is, these magmas were slightly different, and this could play an important role in the reason why the eruption became explosive,” emphasizes Harangi. .

“We identified several amphiboles with chemical composition not reported in volcanic rocks from other volcanoes,” adds Cserép, as an important result of the research. They interpreted this amphibole as an early phase of crystallization in ultra-hydrated magmas, and these water-rich recharge magmas may have played a key role in triggering the explosive eruptions.

The composition of the outermost edge of iron and titanium crystals and oxides provided information on the state of the magma just before the eruptions. Postdoctoral researcher Máté Szemerédi, another lead author of the study, says: “The composition of iron and titanium oxides equilibrates within a few days when the state of the magma changes; they indicate that the erupting magma was at 800-830 degrees Celsius and was oxidized. » .

The importance of the Ciomadul volcano

Currently, the Ciomadul volcano shows no signs of awakening. However, this study also highlights that reactivation can occur quickly, within weeks or months, when recharged by hot, hydrated magma. Quantitative volcanic petrology studies are important to reconstruct subvolcanic magma reservoir structure and magma storage conditions, which can also help us in eruption prediction to better understand pre-eruptive signals.

“This research is new in the sense that it is carried out on a long-dormant volcano and, therefore, the Ciomadul volcano is the subject of increasing international attention,” explains Szabolcs Harangi. This helps to emphasize that in addition to the approximately 1,500 potentially active volcanoes on Earth, long-dormant volcanoes can also pose a previously unknown danger, especially if there is still molten magma beneath them .

The work is published in the journal Contributions to mineralogy and petrology.