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Volcanologist Lukáš Krmíček studied one of world's most active volcanoes. He collected samples directly during eruptions.
In the second half of August, volcanologist Lukáš Krmíček from the FCE embarked on a field expedition to the active Yasur volcano on Tanna Island in the Vanuatu archipelago. Yasur is a persistently active volcano with predominantly Strombolian eruptions. The volcano’s crater contains several active eruptive vents that eject incandescent material during volcanic activity. Explosions occur at intervals of a few minutes, and the ejected material lands in the surrounding area. Volcanic bombs were one of the main targets for sampling.
Yasur is also one of the few places where it is possible to approach an active erupting crater at close range. For field researchers, however, this means extremely demanding conditions. Moving around the crater requires complete concentration, as explosions can eject ballistic projectiles of various sizes in different directions.
“First, you hear a powerful explosion or a series of explosions. Only then does incandescent material start flying into the surrounding area. It is important to stay where you are, or move aside if necessary, and not turn your back on the eruption. You have a few seconds to react. Finally, a huge cloud of volcanic ash rises from inside the volcano. At the same time, it is essential to monitor concentrations of toxic volcanic gases continuously,” says Lukáš Krmíček, describing the conditions during the expedition.
Samples of volcanic bombs were collected by Krmíček directly where they landed. This sampling approach is important for further study: a sample’s location makes it possible to link its properties to the specific conditions under which it was deposited during the eruption. This allows researchers to examine characteristics such as the rock’s porosity, internal structure and mechanical properties.
At Yasur, another intriguing feature is the considerable variability of the bombs themselves. Some have a relatively simple structure and consist of gas-rich material originating from the erupting magma. Others may contain dense inclusions – fragments of previously crystallised lava that were ejected back to the surface during the eruption. The presence of these compact fragments can substantially alter a bomb’s mechanical properties.
“Two bombs may look similar at first glance, yet differ significantly in their mechanical or thermomechanical properties. The decisive factors are their internal structure, porosity, fractures and the presence of older, compact material,” explains Krmíček.
From a Czech volcano to the active Yasur
The research in Vanuatu builds on previous work by researchers from FCE focusing on the mechanical properties of volcanic bombs.
In 2025, the prestigious journal Bulletin of Volcanology published a study entitled Mechanical properties of basaltic volcanic bombs: a case study from the Uhlířský vrch volcano, Czech Republic, which examined volcanic bombs from Uhlířský vrch near Bruntál and the relationship between their mechanical properties and their internal structure, porosity and fractures. At Yasur, the researchers are now applying this approach to samples collected directly from an active volcano.
“At Uhlířský vrch, we confirmed the value of studying the mechanical properties of volcanic bombs systematically. At Yasur, we can extend this approach to material formed by present-day volcanic activity,” says Lukáš Krmíček.
The stability of a volcanic edifice is influenced, among other factors, by the properties of volcanic rocks, the way they are deposited, including individual layers of volcanic ash, and the effects of groundwater and hydrothermal processes, which can alter and weaken rocks along fractures.
Yasur as part of a larger volcanic system
Yasur lies within an extensive volcanic system associated with the older Siwi caldera, which measures approximately 9 × 4 km. The caldera formed in connection with large-scale ignimbrite eruptions. Yasur itself, rising to over 360 metres, lies on the edge of the Yenkahe block, which measures approximately 6 × 3 km and has been rising very rapidly over the past millennium.
The average uplift rate is around 16 cm per year. This is associated with magma accumulation in shallow parts of the volcanic system. Estimates suggest that as much as 25 km³ of magma has accumulated beneath the Siwi caldera over approximately the past 1,000 years. This is not a single continuous mass of molten material, but magma dispersed within the surrounding rock.
The volcanic system is also associated with intense hydrothermal activity. Sulphurous fumaroles, hot spots and other signs of escaping hot gases and fluids occur around Yasur. Hydrothermal processes take place along faults, among other locations, and can chemically alter and weaken rocks. These areas therefore represent another important research focus in assessing the stability of volcanic slopes.
The “Child of Krakatoa” awakens
The field expedition was followed by a trip to Indonesia. There, Lukáš Krmíček attended the international IDRiM 2026 conference in Bali, focusing on natural hazards and their management. At the conference, he presented research describing the mechanisms and spread of fires near active eruptions.
Vanuatu and Indonesia share a similar geological setting. Both are associated with subduction zones, where one tectonic plate slides beneath another. Subduction creates the conditions for the formation of extensive volcanic arcs and is also linked to substantial seismic activity. For example, the Vanuatu archipelago was struck by a powerful magnitude 7.3 earthquake this year.
In Indonesia, the situation in early September was particularly notable in terms of volcanic activity. At one point, as many as six volcanoes were active. Each volcano’s activity was independent of the others.
Before the conference, participants had also planned to visit Indonesia’s Ijen volcano. However, it was closed from 4 September because of ongoing fires in the surrounding area. On the same day, 4 September, significant activity also began at Anak Krakatau, forcing the closure of as many as eight airports in Indonesia. The famous “Child of Krakatoa” emerged at the site of the original volcano following the deafening 1883 eruption, which destroyed much of the island and produced one of the loudest sounds in history. The volcano’s future activity, however, is inherently unpredictable.
Ironically, a volcanic eruption thus disrupted the very meeting devoted to natural hazards. “Because of the Anak Krakatau eruption, some participants were ultimately unable to attend the conference,” adds Krmíček.
Further work awaits in the laboratory
The expedition to Vanuatu and subsequent participation in the conference in Indonesia connected field volcanology with natural hazards research. While the main focus at Yasur was on fresh eruption products, particularly volcanic bombs, in Indonesia Lukáš Krmíček focused on current volcanic activity and its links to other natural hazards.
For FCE BUT, the connection between volcanology, rock mechanics, geotechnical engineering and natural hazards research is particularly important. The samples collected at Yasur now await laboratory analysis. The aim will be to determine how the properties of different types of volcanic bombs vary and what role porosity, internal structure, fractures and inclusions of older rocks play in their mechanical behaviour.
The Yasur samples will also make it possible to compare the properties of material formed during a present-day eruption with findings from research on older volcanic rocks. Field observations combined with laboratory measurements may contribute to a better understanding of the behaviour of volcanic rocks and the stability of volcanic slopes. The findings may also be useful in studying other active volcanoes whose activity affects the lives of people nearby.
Source: FCE BUT
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