LMU volcanologists decipher the behavior of magma beneath an active volcano and reveal how it reacts to drilling.

Although volcanic eruptions are spectacular natural events that occur around the world every day, most volcanoes spend the majority of their time not erupting. To accurately forecast volcanic activity, it’s important to characterise the magma before an eruption is imminent. A team lead by LMU volcanologist Dr. Janine Birnbaum has managed to directly reconstruct the prevailing conditions in a magma chamber for the first time and reveal how magma reacts to drilling. The results, which were published in the journal Nature, provide important insights that could improve the monitoring of magma and pave the way for new applications.

Magma slowly moves from deep within the Earth toward the surface. It often temporarily stops in the crust, where it may reside for years, decades, or even millennia. In that time, it cools, crystallizes, ingests the surrounding crustal rocks, and loses or gains dissolved gases – primarily water and carbon dioxide – that power volcanic eruptions. An eruption occurs when the magma system is perturbed through the addition of heat, new magma from depth, or the formation of bubbles – like an overheated can of soda that expands and eventually bursts.

Drilling in Krafla volcanic field in Iceland

To understand how volcanoes behave between and before eruptions, it is important to have detailed information about the temperature, pressure, and gas content of the magma in the Earth’s crust. However, magma often resides deep below the Earth’s surface and is not accessible to direct measurements.

For their new study, the researchers exploited the fact that magma beneath the Krafla volcanic field in the northeast of Iceland comes surprisingly close to the surface. During operations at the Krafla Geothermal Station in 2009, the Iceland Deep Drilling Project 1 (IDDP-1) well unexpectedly intersected a magma body at a depth of just over 2 km. Cold drilling fluids dumped water on the magma, quenching it into tiny chips of glass.

When researchers looked at these chips, they encountered a puzzle: Although the quenched magma had many small bubbles, it held less dissolved gas than the magma was capable of holding at the expected temperature and pressure. To solve this question, the LMU researchers used a new numerical model which showed that the magma reacted to the drilling and lost gas before it fully solidified into glass. Previous measurements had shown that the magma requires several minutes to cool from an initial temperature of about 900 °C to become a glass at around 520 °C. According to the researchers’ hypothesis, this gives the gas enough time to escape from the melt and to cause the observed bubbles to form.

Gas escapes within five minutes

As such, the gas content in the chips of glass does not reflect the original conditions, but is the product of this dynamic process. “It’s like a blurry photo,” explains Birnbaum. “But if we know our exposure time and how fast our system moves, we can unravel where it started.” By simulating how fast the gas escapes, the researchers were able to reconstruct the original gas content. This revealed that the ‘missing’ gas was lost in under five minutes during drilling.

According to the researchers, these findings can help make future endeavors in geothermal fields on active volcanoes safer, while also paving the way for targeted drilling into magma for purposes such as monitoring and green energy extraction.