Nestled between lava and the lab: Dr Harri Geiger researches volcanoes worldwide
Freiburg, 03.09.2025
Anyone who talks to Dr Harri Geiger quickly discovers that his enthusiasm for his research is contagious. The petrologist and geochemist at the Institute of Earth and Environmental Sciences in Freiburg wants to find out how volcanoes work and explain why their behaviour plays a greater role in our lives than most people realise.
Geiger travels extensively to places such as Iceland, the Canary Islands, Indonesia and Chile where he collects lava, analyses rocks and makes the invisible visible – the processes deep beneath the earth.
From electrical engineering to geoscience
His career path was by no means predetermined. Geiger initially began studying electrical engineering and computer science at Jacobs University (now Constructor University) in Bremen. It was an excursion with geoscientists that changed everything: “I realised that rocks and the stories they tell fascinate me much more.”
He switched majors, completed an additional bachelor’s degree in geoscience, went to Sweden for his master’s and doctorate, and returned to Germany five years ago for the position at the University of Freiburg. Today, he combines his technical training with geology: data from microscopy, chemical analyses and modelling are just as important to him as fieldwork at the volcano.
Why volcanoes are more than just a natural spectacle
For many people, volcanoes are spectacular images you see on the news. For Geiger, there is much more to it than that. “Volcanic eruptions are not only photogenic and exciting, they also have far-reaching implications for us as humans and for the planet. Eruptions can threaten people and infrastructure, but at the same time, volcanic soils are fertile and productive. Many of the metallic raw materials we need for mobile phones and laptops come from magmatic processes, and even the climate can be changed by volcanic eruptions.” With his research, Geiger not only wants to better assess the dangers, but above all to understand how our planet works.
“A piece of lava is like a diary. These rocks are more than dead matter, because they tell stories of processes deep within the Earth that influence our lives on the surface. Understanding this is what drives me every day.”
Dr Harri Geiger
Petrologist and geochemist at the Institute of Earth and Environmental Sciences
Lava fountains and flows, as well as some very high eruption columns consisting of gases and ash, were typical features of the 2021 Tajogaite volcanic eruption on La Palma. Photo: Harri Geiger
A lava flow from the 2021 Tajogaite eruption on La Palma, near Todoque. As toxic gases escape from the lava, protective equipment is mandatory when working on the active lava flow. Photo: James Day
Many buildings and infrastructure were destroyed by the volcanic eruption. Vehicles that were not removed in time also stood no chance against the lava, which was over 1,000 degrees Celsius. Photo: Valentin Troll
For the 38-year-old, the eruption on the Canary Island of La Palma in 2021 was an unforgettable experience. It was the first time he had seen an active volcano up close. “Observing volcanic processes live and not just seeing cooled rocks in the laboratory was very impressive.” It had been clear for years that an eruption was imminent, but no one knew exactly when and where.
Volcanoes and their significance
- Climate: Large eruptions can change the atmosphere and cool the global climate.
- Raw materials: Metals in smartphones and computers are created by processes inside the Earth.
- Risks: Millions of people live in close proximity to active volcanoes. There are approximately 1,350 potentially active volcanoes worldwide. Around 500 have erupted in the last 10,000 years. Between 40 and 50 volcanoes erupt every year.
- Magmatic: Magmatic processes describe the formation, movement and cooling of magma – the hot molten rock from the Earth’s interior. They are the basis for volcanism and are crucial for the formation of many mineral resources.
Stones as historical witnesses
What looks like a grey lump to laymen is an archive full of information for Geiger. “A piece of lava is like a diary. Based on the chemistry of the crystals it contains, I can tell at what temperature and pressure they were formed. These rocks are more than dead matter, because they tell stories of processes deep within the Earth that influence our lives on the surface. Understanding this is what drives me every day.” Clues can already be found in the terrain itself. Whether lava solidifies in rope-like or sharp-edged formations reveals something about its viscosity – in other words, how fluid or viscous it was. From this, insights into the eruption processes and dynamics can be derived.
Research in international teams
When a volcano erupts somewhere, Geiger meets colleagues from all over the world. “Everyone brings special expertise to the table – be it analytics, seismic data or geochemical modelling. Together, we can paint a much bigger picture.” The Freiburg institute has state-of-the-art equipment, which has been completely overhauled in recent years. “We really do have the latest analytical technology on site, which helps us enormously.”
Geiger was most recently in Iceland, where a series of eruptions has been occurring on the Reykjanes Peninsula since 2021. “We sampled the most recent lava, often off the beaten track, which often involve lengthy treks. The rock samples are then distributed worldwide from Freiburg, Uppsala University and the Swedish Museum of Natural History in Stockholm to the University of Iceland, Cornell University and the Scripps Institution of Oceanography at the University of California in the USA and the University of Cape Town in South Africa.
Between lecture hall and volcanic field
Back in Freiburg, Geiger teaches students, supervises theses and evaluates data. He also works on site at the nearby Kaiserstuhl to study volcanic deposits and understand the processes that took place 14 to 18 million years ago. “The Kaiserstuhl is famous because it is one of the few places in the world where carbonatite occurs – a very rare magmatic rock.” But as soon as an eruption occurs somewhere, the plan changes. “Then flights, permits and equipment have to be arranged. Everything is fast-paced. But that’s exactly what makes the job so versatile.”
A look to the future
The big questions remain: Can a volcanic eruption be predicted? When and where exactly? “We are still a long way from being able to make accurate predictions. But we are constantly learning from new eruptions in order to better interpret small earthquakes and ground uplifts. What we are now researching more intensively is how volcanoes change during an ongoing eruption.”
A paradigm shift: In the past, it was assumed that there was one large magma chamber beneath volcanoes. Today, research is based on the assumption of a dynamic system of many small chambers. Geiger’s analyses also confirm this. “The chemistry of the magma changes during an eruption. If we can begin to understand how and what effects this has, we will be one step closer to being able to predict eruptions.”
Volcanoes and society
- Risks: In Indonesia in particular, millions of people live close to active volcanoes – early warning systems are crucial.
- Opportunities: Volcanic soils are fertile and provide raw materials and geothermal energy.
- Fascination: Volcanoes combine the forces of nature with scientific curiosity – one reason why researchers such as Geiger have spent their entire lives studying them.
For Geiger, science communication is key through school classes, lectures and field trips. “When students are out in the field and suddenly see that the theory from their lectures makes sense, it is often an eye-opening experience.” Volcanic research is not just basic research, it also has a direct impact on society. It contributes, for instance, to our understanding of climate change.
Major eruptions have changed the climate in the past, as gases and ash particles emitted during volcanic eruptions can disrupt the atmosphere and thus influence the temperature on Earth in subsequent years. Conversely, when global warming causes glaciers to melt and thus changes the pressure on the underlying crust, this can lead to more frequent new eruptions, which in turn can pose dangers. These observations are part of a greater puzzle.