Earthquake swarm continues, more than 2000 quakes during past 48 hours
Update Mon 15 Mar 2021 06:41
The volcano-seismic unrest continues on the southern Reykjanes peninsula, centered around Fagradalsfjall mountain.
Earthquakes on the Reykjanes peninsula during the past 48 hours (image: IMO)
A strong mag. 5.4 earthquake occurred yesterday 14 Mar 2021 at 2:15 pm local time 5.4 km SW of Fagradalsfjall. It was widely felt in the area, and even captured by the webcam:
Likelihood of volcanic eruption near Fagradalsfjall increases by the day
Update Fri 12 Mar 2021 16:06
Recent earthquakes in the Reykjanes peninsula
The earthquake swarm in the Reykjanes peninsula, concentrated in the area around Mt. Fagradalsfjall SW of Keilir, continues with no signs of weakening. By early afternoon, the Iceland Met Office (IMO) had already recorded over 1700 earthquakes since midnight alone, including many of magnitude 3 or higher and a widely felt magnitude 5 event at 07:53 GMT this morning.
Latest satellite images and GPS data show that accumulation of magma is concentrated at the southern part of the dike beneath Mt. Fagradalsfjall. This is the most likely site for a possible eruption. InSAR image reflects changes between March 3 to March 9 2021. Image contains modified Copernicus Sentinel data  (image: IMO)
This seismic activity has been identified as result of continuing influx of magma into a newly forming dike (sheet-shaped magma reservoir) at shallow depth, of only about 1km beneath the surface in places. The longer it continues the higher the likelihood of it breaching the surface, or in other words causing a volcanic eruption.
Icelandic scientists concluded that "the dike intrusion is expanding with the most active magma flow centered at the southern part of it. A volcanic eruption remains a possibility as magma is still flowing into the corridor. With the ongoing activity the probability of an eruption increases day by day. It is considered very unlikely that lava from a possible eruption would reach populated areas.
The latest report by IMO further states:
- It is important to follow the activity in the southern region of Mt. Fagradalsfjall in order to evaluate whether the dike is expanding to the south.
- Latest satellite images and GPS data show that accumulation of magma is concentrated at the southern end of the dike beneath Mt. Fagradalsfjall. This is currently the most likely site for a possible eruption.
- If the dike keeps expanding and increasing stresses in the area, continuing earthquake activity that can be felt in populated areas is expected.
- Currently, the magma is shallow, lying 1-1,5 km beneath the crust. Therefore, it can be expected that an eruption could start without a strong precursory signal, as the magma can easily brake through the last hundreds of meters of the crust once the critical pressure is reached. From experience of lava flow eruptions (as we might expect), the eruption tremor is weak and has a low amplitude. For this reason, the IMO has installed webcams which can be used to monitor the area, in case of an eruption will start without clear precursory signals.
Geophysical survey leads to visualization of magma chamber under Reykjanes Peninsula
Update Thu 11 Mar 2021 07:30
In recent reports, the Icelandic Meteorological Office (IMO) stated that magmatic movements are the likely cause of the ongoing earthquake swarm in the Reykjanes peninsula. As magma migrates upwards, overlying rock layers are displaced, which causes tremors and ground deformation on the surface.
Sketch showing the forming magma reservoir, a dike, under the Reykjanes peninsula (image: RUV)
Geophysical surveys were conducted along the area of unrest located in between Fagradalsfjall and Keilir. The results generated a detailed look at how the expanding magma chamber under the Reykjanes peninsula behaves.
Expanding magma chamber under the Reykjanes peninsula
In an interview of the Icelandic National Broadcasting Service (RUV) with geophysicist Freysteinn Sigmundsson on 9 March 2021, the growing magma reservoir was shown to be in the form of a dike: It is currently about 1 meter wide and 7 kilometers long spanning the length between Keilir at the northern end and Fagradalsfjall at the southern end. The bottom of the magma chamber is located 5 kilometers below ground surface and is the site for magmatic influx. This is the process by which magma flows from deeper sources in the mantle towards the shallow magma chamber where it is now being stored.
15-20 cubic meters of magma flowing into the reservoir
Based on the rate of deformation, allowing to estimate the increase of volume of the dike, the magma influx was measured to be about 15 to 20 cubic meters per second.
The northern end of the magma chamber lies 2 kilometers deep under Keilir, while the southern end lies only a kilometer deep under Fagradalsfjall. Due to this orientation of the magma chamber, geophysicists believe that it is possible that the magma underneath Keilir may have already cooled down and solidified or is about to. An eruption in this area is thus less likely than in the area of the southern end of the dike, i.e. near Fagradalsfjall. It also means that there are more seismic and magmatic activities at the southern end near Fagradalsfjall.
Greatest volcano-seismic activity near Fagradalsfjall
According to geophysicist Sigmundsson, if magma continues to flow into the magma chamber, it will expand into the area with least resistance. This means that the magma chamber will expand southward as that portion is closer to the surface. Magma might eventually reach the surface causing an eruption near Fagradalsfjall. Scientists found evidence of magma migration such as increased seismic activities and ground deformation in the area.
However, there is still no way of knowing whether this scenario (of an eruption at the surface) becomes true, and if yes, what the exact date and time for an eruption in the area will be. There is still the possibility that the current volcano-seismic activity will weaken and no eruption occurs. But Sigmundsson believes that if an eruption does occur, it will be similar to the 2010 Fimmvorduhals fissure eruption, producing lava fountains and voluminous lava flows, but not followed by an explosive stage as there is no nearby glacier or larger water body that might interact.
For the complete interview with geophysicist Freysteinn Sigmundsson, visit the RUV news page here.
More than 34,000 quakes in two weeks
Update Wed 10 Mar 2021 15:29
The Icelandic Met Office (IMO) announced earlier today, that the total number of earthquakes in the region has exceeded 34,000 since the onset of the seismic swarm about 2 weeks ago.
Earthquakes on the Reykjanes peninsula during the past 2 weeks (image: IMO)
For comparison, it had about 3,400 quakes in the whole of 2020, which also had shown elevated activity, while the average during the previous years was in the range of 1,000-3,000 quakes per year.
Aviation warning and future possibilities
Update Wed 10 Mar 2021 06:08
Figure 1. Earthquake location map as of 10 Mar 2021. Recent earthquakes focused in areas between Fagradalsfjall and Keillir. (source: IMO)
As the number of earthquakes recorded in the Reykjanes Peninsula, Iceland, surpassed the 20,000 mark, the main area of unrest was identified as the area between Fagradalsfjall and Keillir. According to the Icelandic Meteorological Office (IMO), magma intrusions under the surface are the prime suspect to cause this ongoing seismic activity.
Figure 2. Aviation color code map of Iceland. Green – volcano in non-eruptive state, Yellow – elevated unrest, volcanic activity decreased, Orange – heightened unrest, increased likelihood of eruption. (source: IMO)
However, there are still uncertainties as to how these volcano-seismic events will develop. IMO listed the possibilities in their website here:
- The earthquake swarm might slow down in the following days and weeks, or the contrary may occur: it could increase in intensity and result in quakes of magnitudes of up to 6.0 in the area.
- If the latter occurs, an earthquake with a magnitude as high as 6.5 could hit the nearby volcanic system roughly 20 km east from the main area of unrest.
- If magma intrusion resumes, an effusive volcanic eruption could occur resulting in lava flows which will not threaten inhabited areas on the peninsula.
- The magma intrusion may also stop, in which case magma will solidify in place underground without an eruption at the surface.
In the meantime, IMO raised aviation warnings over the Krysuvik volcanic system in southwestern Iceland and the Grimsvotn volcano located in Vatnajokull National Park in southern Iceland. Orange volcano warning was raised over Krysuvik, and yellow warning over Grimsvotn. In June 2020, scientists reported high levels of sulfur dioxide coming from Grimsvotn. This is an indication of the presence of magma at shallow depth. IMO warned of a possible violent phreatic eruption, which could result from melting ice interacting with the hot magma.
For more information on the aviation color codes for Icelandic volcanic systems, visit the IMO website where they will post updates on this matter.