All indications are that the volcanic eruption that began Monday night was just a lightning event on the Reykjanes Peninsula, and in a few days the scene will be calm again. All of this means great relief for the thousands of people who lived in Grindavik that the lava will not dislodge their homes, and there is also hope that they will be able to celebrate at home. Meanwhile, it was possible to determine the chemical composition of lava rocks spread on the surface as quickly as possible, within 24 hours, and petrographic and geochemical data could serve as an explanation for why the volcanic event was so short-lived.
The initial intensity of the eruption that occurred in the Sundhnúkur rift zone, when 100-200 cubic meters of magma flowed to the surface per second, suggests that it could last for weeks or months, however, after a strong start, the nature of the eruption changed very quickly. After the lava curtain of the 4-kilometre-long active fissure on Monday night, magma dispersed in only a few places on Wednesday, and the lava reddened in only a few places on Thursday morning. Based on recent satellite images, the lava field is now 3.7 square kilometers in size. A lot or a little? In size, it rivals the lava field of the first Vajradasfjall eruption of 2021 which lasted several months (Geldingadallir eruption 4.6 km).2 area), but it is much larger than the Miradalir eruption in 2022 and the Letli-Hrutot eruption this year. Of course the picture is a bit deceiving, because the previous pictures took place in a mountainous area, where the thickness of the lava can reach tens of meters in many places, but here a thin layer of lava has formed. In terms of volume, this is a far cry from the yield of previous volcanic eruptions, and according to first estimates, only a few million cubic meters of lava could be spread over the flat surface.
Why could there be so little volcanic activity after all this waiting? The answer lies in lava rocks. In record time, within 24 hours of the eruption, geologists from the University of Iceland analyzed and reported on the chemical composition of the magma fueling the volcanic activity, the rock glass representing the molten rock, and the lava rocks. A key role in this was played by Eniko Palli, who obtained her degree and PhD at the Department of Geology and Geochemistry at TTK ELTE in Budapest, in the Csaba Szabó group. He has been an associate professor at the University of Iceland for a decade, and has used his scientific expertise gained during his postdoctoral work at home and abroad to explore the causes of many volcanic activities.
What does this rock composition data show and why is it interesting? The chemical composition of the magma, especially the proportion of potassium and titanium dioxide, does not resemble the magma of previous eruptions in this area, a few thousand years ago, but rather the magma that fueled the Vagradalsfjall eruptions in recent years. So it appears that there may be a common magma reservoir forming somewhere at the top of the Earth’s mantle or at the bottom of the Earth’s crust, which is causing these eruptions. But why didn’t more magma come out, why didn’t the volcanic eruption last longer? A notable feature of the chemical composition of lava rocks is its relatively low magnesium oxide content. This substance indicates very sensitively the development of the magma, that is, the degree to which it has undergone crystallization. During crystallization, the composition of the remaining melt and thus its physical properties change. Now, relatively advanced magma has burst to the surface, and is much more advanced than in recent years. Based on all of this, the possibility of a rapid course of the eruption actually exists, especially since the intensity of the eruption decreased quickly, that is, there was no new magma to feed it.
It is likely that during this week’s eruption, magma was pushed sideways about 15 km to a depth of 1-2 km and spent a few weeks in the Sundhnokur Hills area on November 10-11 during the eruption. Many earthquakes appeared on the surface. Here, the magma is laid out lengthwise, but with a small width and thickness. A few weeks were enough for it to crystallize as the temperature dropped, so the more developed magma exerted pressure that eventually broke through the rocky body above it. During the eruption, 4 km of magma rose to the surface. In the present case, this was the amount of magma actually suitable for an eruption, and the more powerful the crystalline magma remained in the Earth’s crust.
However, it must be emphasized that this is not the end of the whole story. Before the eruption, Svartsinje and the area west of it showed continuous surface uplift. This was also confirmed by the recent radar image taken by the satellites (InSAR), and it is clear that the reason for this may be the pressure of magma accumulated in the Earth’s crust. The depth of the magma can reach 5-7 kilometers and melting of new rocks can come from here at any time, which can lead to a volcanic eruption. Icelandic experts unanimously confirm that the question is not whether there will be another volcanic eruption on the Reykjanes Peninsula, but when and where magma will erupt again. Therefore, specialists continue to monitor signals coming from the depths and the rise of the surface, because there may be relief now, but another volcanic season will soon follow. Until then, there will be something to evaluate, and this scientific experiment will mean a lot in monitoring and predicting upcoming volcanic eruptions. This is what science provides, and this is what volcanic knowledge provides, which produces rapid scientific data and derives its interpretation.
The author is a volcanology geologist, Corresponding Member of the Hungarian Academy of Sciences, Institute Director, University Professor, and Research Group Leader, ELTE TTK Institute of Geography and Earth Sciences, Department of Geology and Geochemistry, Hungarian Academy of Sciences – ELTE Volcanology Research Group
