Frozen magma filled-fractures allow a peak into the volcano

Volcanoes are some of the most hazardous, yet least predictable natural phenomena of our planet. To understand the processes that operate inside volcanoes, geoscientists frequently study solidified, magma-filled fractures, so-called dykes. Dykes are the main transport channels for magma in the Earth's crust and control the growth of magma reservoirs and the size of volcanic eruptions. Comprehending how dykes form and propagate is therefore vital to our understanding of volcanoes. An international team of scientists led by researchers from Uppsala University published a study in Nature Communications, which reveals that it is the strength of the rock surrounding a magma reservoir that controls the size of dykes to form

The researchers measured the thickness of thousands of dykes on Iceland and in the Canary Islands over several months of fieldwork. Back home, they rigorously analysed the data with statistical methods and were astonished:

“We were surprised that all our datasets showed the same statistical distribution. Neither the type of volcano, nor the type of dyke seems to play a major role. It was always the Weibull distribution that fitted best” says Michael Krumbholz, a researcher at the Department of Earth Sciences at Uppsala University.

The Weibull distribution is well-known in materials science and is named after the Swedish scientists Waloddi Weibull who obtained his Honorary doctorate from Uppsala University in 1932. The Weibull distribution is also known as the “weakest link of a chain” principle and mathematically predicts that a material will break first where it is weakest. Since two samples of the same material are never absolutely identical due to e.g. microcracks or impurities, they are therefore never of equal strength.

“The surprisingly good fit of the Weibull distribution to our data gave us the hint” says Christoph Hieronymus, Senior lecturer at the Department of Earth Sciences, Uppsala University. “It suggests that the strength of the rocks surrounding the magma chamber controls when and how dykes form. This makes a lot of sense now, as the magma will first break the surrounding rock were it is weakest.” 

“Our results also underline that the strength of rocks in the Earth’s crust in general is not equal in all places” summarize Krumbholz and Hieronymus. “Even though rocks differ from many man-made materials, they still follow the rules of material science and that means rock strength follows a Weibull distribution too.”

The research team is now hoping to apply these findings to volcano monitoring and eruption forecasting.