Geldingardalsgos Eruption Event, Iceland, March 2021

Hello Planetary Pals,

In the past month, an eruption has been predicted to occur in the Southwest of Iceland. On March 19th, that eruption began, spewing out hot basaltic lava. Given that my research is focused on basaltic lava fields in Iceland, I decided to write my blog post this week about this new eruption event.


In the area, there have been earthquakes up to M5.6 since late 2020. This was thought to be the start of a reactivation of the Reykjanes tectonic- volcanic system. The last known major eruption in the area is from the 13th century. Seismic activity increased again in mid-late February. All earthquakes occurred with epicenters on the Reykjanes Peninsula, but could be felt throughout the area. At this point, it was unknown if a magma body was surfacing, though it was suspected. Give the proximity to the capital, it was important for geologists and natural disaster monitors to understand the seismic activity and predict any possible volcanic risk to the region, population, and infrastructure.  

By March 1st, continued interferometric satellite radar studies of the Reykjanes Peninsula continued to show extensive ground deformation that indicated a magma body must be present; the seismic disturbances were too many and too great to be from tectonism alone. As a magma body buoyantly rises, it creates many earthquakes as it displaces and squeezes through the bedrock. They pinpointed that the Fagradalsfjall area to be most susceptible to eruption and continued to issue earthquake warnings for the entire region. Continued tremors by March 9th indicated that the magma body was expanding. At this point, it was still unknown whether the magma would slow and solidify underground or if it would rise and erupt effusively.

Geophysical surveys across the Reykjanes Peninsula were conducted to figure out the size and depth of the intrusion. The magma body was discovered to be quite shallow, only about 1km below the crust. This means that there would be little warning if and when an eruption was commencing. Given the orientation of the intrusion, the eastern end was thought to have cooled and solidified, while the western end, which was closer to the surface was hypothesized to be able to erupt. Many thousands of earthquakes continued in the following weeks.

On the evening of March 19th effusive lava was spotted coming from Geldingadalur nearby the Fagradalur mountain. It was not accompanied by any major earthquake but began slowly leaking out of a 500 meter long fissure near the mountain. It began with two small channels of lava moving out from the vent and also featured small lava fountains and spatter cones. The main spatter cone would later collapse unexpectedly. Volcanic gasses were not cause for worry with such a small eruption, though nearby communities were told to stay indoors to avoid risk. There is also minimal risk to air travel nor infrastructure. As well, earthquakes have been steadily decreasing in frequency and intensity. There is risk to an archaeological site nearby, however and archaeologists have been attempting to excavate the site before it get buried beneath the lava flows.

As of Sunday, the thickness of the lava flow is roughly 10m and it covers an area of 0.1 km2  (compare to Holuhraun which is 85 km2). It is currently unknown how long the eruption will last, however similar sized eruptions took weeks or even months to exhaust the 50,000,000 m3 magma chamber. At the current rates, the magma would be erupted fully within a couple weeks. The eruption at Fagradalsfjall has been named Geldingardalsgos. The site is being monitored, tested, and mapped via satellite and in-situ measurements. New fissures can open up, but it is not known if and when they will.

Published by Anthony Dicecca

Hello and welcome to my blog. I am Anthony Dicecca, and I am currently pursuing a thesis-based Masters degree in Geology with a Specialization in Planetary Science and Exploration. I am a native of Rochester, New York but moved to London, Ontario to attend the University of Western Ontario. From 2016 to 2020 I worked to complete my undergraduate degree, finishing with a BSc in Physics and a BSc in Geology. During this time I developed a passion for geology, and in particular, planetary science. I've had the pleasure of working with Dr. Gordon Osinski and his team during this time aiding in research ranging from Arctic peri-glaciology to global impact cratering, and from Lunar spectroscopy to Martian mapping. In Autumn 2020 I continued my education at the U.W.O., working towards a MSc in Geology with a Specialization in Planetary Science and Exploration. My research will likely involve insights obtained from the Holuhraun Lava Field in Iceland and their applications to other bodies in the Solar System. This blog serves as an archive of my progression over the next few semesters.

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