Considerable seismic activity continues at the Reykjanes peninsula, Iceland, with more than 6 000 earthquakes manually checked since the beginning of the year. According to the Icelandic Met Office (IMO), this is the most intense activity ever recorded in the region since the beginning of digital monitoring in 1991. Data indicates the activity is affecting all volcanic systems in the Reykjanes peninsula and Reykjanes ridge. In addition, GPS measurements, as well as detailed analysis and model calculations of the available data, now give evidence of a new magma deposit west of the Reykjanes peninsula under Rauðhólar and Sýrfell.
Recent data show that uplift has started again, with the center just west of Mt. Thorbjorn, IMO reported on April 2, 2020. Uplift was measured from January 22, 2020, until the beginning of February and has started up again during the first half of March.
During the first sequence in January-February, the deformation rate was about 3 – 4 mm (0.11 – 0.15 inches) per day with a total of 6 cm (2.3 inches) uplift during the whole period.
In the sequence that is ongoing now, the deformation rate looks to be only half of what it was (or even slower). In total, the uplift is about 7 – 8 cm (2.7 – 3.1 inches) since the end of January.
The Scientific Advisory Board (SAB) who met on March 28 still believes that the most likely explanation of the uplift is a magma intrusion where the magma is 'forcing' its way horizontally between the stratum in the crust and forming a thin sill at about 3 to 4 km (1.8 – 2.5 miles) depth. The magma intrusion causes a considerable amount of earthquakes in the area north of Grindavík. Their next meeting is scheduled for April 8.
A model of the ongoing magma intrusion shows that fissures can open in the uppermost layer of the crust, at 1 – 2 km (0.62 – 1.24 miles), because of the tensional stress induced by the uplift itself. This change in the crustal stress might lead to more earthquakes related to injection at boreholes, which was not common before in the area, IMO said.
The work procedure for the injections will be reviewed in collaboration with HS-Orka and discussion will be taken on how is the best way to monitor the earthquakes likely due to these changes, it added.
On Saturday, March 28, an earthquake swarm occurred in Eldey, indicating that the activity is affecting all volcanic systems in the peninsula and the ridge, eg. from Eldey all the way to Krýsuvík.
The interpretation of these events is still uncertain, but there are indications that a common underlying process is the cause of the activation of such a widespread area in such a short timeframe.
However, the Reykjanes peninsula and the Reykjanes ridge are composed of plate boundaries. Also, the Eldey, Reykjanes, Svartsengi and Krýsuvík volcanic systems lie right across the boundaries.
Because of the activity ongoing in the area, the SAB believes that it is extremely important to monitor and investigate the ongoing activity in the Reykjanes peninsula as a whole, and compare this activity with older events in the area to try to decipher the reasons and identify possible developments.
In addition, GPS measurements, as well as detailed analysis and model calculations of the available data, now give evidence of a new magma deposit west of the Reykjanes peninsula under Rauðhólar and Sýrfell.
"The data we have processed indicates that the magma insertion has taken place from mid-February until the first week of March. This picture was better explained when we got data from the University's GPS measurements, which are not directly related to our monitoring system — meaning that we did not detect this until now," says Kristín Jónsdóttir, Group Director of Nature Conservation at the Icelandic Meteorological Office.
A model places the magma insert at a depth of about 8 – 13 km (5 – 8 miles), which is probably at the bottom of the Earth's crust at considerably more depth than the two magma deposits at Thorbjörn.
"This magma deposit under Sýrfell is the third magma deposit we report on the Reykjanes peninsula since the turn of the year. The presence of this magma insert supports the Resolution of the Swedish Civil Defense Council that it is necessary to look at the activity in the Reykjanes peninsula comprehensively, and not only from the local activity around Svartsengi and Reykjanes," Kristín said.
Featured image credit: IMO
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