New understanding of ultra-rapid formation of magma filled cracks in the Earth


Iceland dataset and models of recent magmatic activity leads to new understanding of ultra-rapid formation of magma filled cracks in the Earth

On 10 November 2023 the town of Grindavik in Iceland was evacuated when massive amounts of magma abruptly started to flow into a magma filled crack that propagated under the town. Magma was emplaced in a ’vertical sheet’ in the Earth’s crust from about 1 to 5 km depth, 15 km long, that widened by up to 8 meters. At the surface, major fault movements and cracking occurred, causing widespread destruction of infrastructure and property. Most of this occurred over a period of about 6 hours, when estimated magma flow rates were ultra-rapid, above 7000 cubic meters per second. This is revealed from detailed observations and interpretation of ground motion, constrained by monitoring of earthquakes, in a new study published in Science, by an international team of investigators lead by University of Iceland and the Icelandic Meteorological Office. The lessons learned are used to explain how super long magma filled cracks, more than tens-of-km long, can form through the combined effects of a large fracture forming on the boundary of a subsurface magma domain, and the effects of extensional forces, that can accumulate in the crust over centuries, for example by the process of plate spreading. Such extensional forces can effectively drive magma into cracks. In the affected area in and near the town of Grindavik, additional, but smaller scale opening of magma filled cracks occurred in December 2023 and January 2024, but in these cases hazardous fissure eruptions occured, causing further destruction of the town of Grindavík. A third eruption began in the morning of today, 8 February 2024. More activity is expected.

Sonja Greiner

Sonja Greiner, PhD student at Department of Earth Sciences, Mineralogy Petrology and Tectonics, has been involved in the study that just has been published in the scientific journal "Science". 

What was the greatest find of the study?

- The most important finding of the study is that very large amounts of magma can begin to move very quickly without needing large overpressure, if there is a lot of tension in the Earth’s crust. In Iceland and specifically on the Reykjanes Peninsula, this tension builds up over hundreds of years due to plate spreading, while the Eurasian and the North-American continental plates slowly drift apart.   

What was your contribution?

- I contributed to this study in helping with the creation of figures, especially the conceptual figure in Figure 5c. I was also preliminarily involved with the development of the physical model and with writing. A part of my PhD project is to look at the coupling of tectonics and volcanism in this area of Iceland, so this topic is very important to me from a scientific point of view.

What can these findings lead to?

The event in November 2023 was the first of (so far) four magmatic intrusions. Although this first event did not end with an eruption, the other three did. The most recent eruption began on 8 February, so only this morning. The event in November helped us to better understand a volcanic system which has not been active for almost 800 years. It also helped to better prepare for hazards and risks associated with the eruptions which happened since then and potential future activity. Lastly, the observation of very high flow rates can possibly help to explain how so called “giant dike swarms”, magma-filled cracks, which can be more than hundreds of kilometers long, can form. This is important not just for Iceland, but for volcanism that happened in other places all over the world.

Publication available here, open access for all for two weeks):

Science magazine home page:

under rubric 'FIRST RELEASE‘ artices

or directly here:

Contact person: 
Freysteinn Sigmundsson, Research Scientist in Geophysics., email:, tel +354 8934607

Sonja Greiner, PhD student in Mineralogy Petrology and Tectonics:

News from the Department of Earth Sciences

Last modified: 2022-09-30