Chemical analysis shows that the lava in the Sundhnúksgígar eruptions comes from multiple reservoirs

• A new study by Icelandic and international scientists was published yesterday in Science
• The findings suggest that it may prove difficult to predict eruptions in the region and how they will behave

The chemical composition of lava from the first four eruptions at Sundhnúksgígar on the Reykjanes peninsula suggests that it originated in multiple reservoirs, located close to each other at a depth of around five kilometres. This means that it may prove difficult to predict when future eruptions will occur and how they will behave. These are the findings of a study led by a team of scientists from the University of Iceland’s Institute of Earth Sciences, in collaboration with the Icelandic Meteorological Office. A paper about the findings was published yesterday in the prestigious journal Science.

As most people are aware, there has been ongoing volcanic activity on the Reykjanes peninsula since 2021.  The first eruption occurred at Fagradalsfjall, but towards the end of last year, an eruption began at Sundhnúksgígar after a large dike formed suddenly under the area in November. A total of six eruptions have occurred at Sundhnúksgígar, but the article in Science is based on data from the first four, i.e. the eruptions from last December, January, February and March, the last of which continued into May.

The goal of the study was to gain a better understanding of how magma accumulates before each eruption by chemical analysis of the erupted lava. If compositions are variable in each eruption, this would indicate that multiple magma reservoirs are contributing to each eruption.

More samples collected than in previous studies

While the four eruptions were happening, scientists collected lava samples from across the lava field, with the aim of finding out whether there were variations in the chemical composition of the lava. They collected a total of 161 samples, which is considerably more than in most other studies. The samples were analysed at the UI Institute of Earth Sciences and the Laboratoire Magmas et Volcans at the Université Clermont Auvergne in France.

The analysis revealed that the chemical composition of the lava varied considerably, suggesting that it did indeed come from several different reservoirs at a depth of around five kilometres beneath Svartsengi. The nature of the variability also changed from one eruption to the next, meaning that the magma accumulation reservoir is likely changing over time.

“Since there are potentially many magma reservoirs being supplied with magma beneath Svartsengi, it may be difficult to predict when future eruptions will occur, and the behaviour of the eruptions may change. For example, how much magma comes out during each eruption, and how long it lasts for, might change depending on which reservoirs supply each eruption,” explains Simon William Matthews, a research specialist in geochemistry at the UI Institute of Earth Sciences and first author of the Science article. 

Simon also points out that it is likely that magmas accumulating in multiple reservoirs in close proximity is a common feature of volcanoes, but this is the first time it has been confirmed for a volcano like Sundhnúksgígar, thanks to the team’s meticulous lava analysis. This research proves that chemical analysis of lava provides more detailed, but complementary, information about volcanoes than geophysics alone.

The study was conducted by a team of scientists from the UI Institute of Earth Sciences and the Icelandic Meteorological Office, working in partnership with scientists at the Laboratoire Magmas et Volcans at Université Clermont Auvergne in France and GeoZentrum Nordbayern at the Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany. The work was funded by a Rannís Grant of Excellence, awarded to Enikö Bali, Halldór Geirsson and Sæmundur Ari Halldórsson, scientists at UI and principle investigators on the project. 

The article can be found on Science´s website.