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Earthquake swarm, uplift west of Mt. Thorbjorn volcano continues, Iceland

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Earthquake swarm and uplift west of Mt. Thorbjorn, Reykjanes Peninsula, Iceland continues on February 1, 2020. However, it is most likely that this activity will stop without any volcanism, the Icelandic Met Office (IMO) said. The last known eruption was during Reykjanes fires, which occurred between 1210 – 1240.

Yesterday evening at 22:22 UTC, a M4.0 earthquake occurred approximately 5 km (3.1 miles) NE of Grindavik and another one M4.3 at 22:24.

Over 700 earthquakes have been measured since 12:00 UTC on January 31. However, no signs of volcanic tremor has been detected, IMO noted at 14:51 UTC today.

Over 100 I-felt-it reports have been received from Reykjanes, the capital area and north to Borgarfjordur. These are the largest earthquakes since the activity started on January 21.

The latest GPS processing shows that the uplift west of Mt. Thorbjorn is still ongoing. In total, the uplift is over 4 cm (1.5 inches) since January 20.

"The most likely explanation of the uplift and earthquake activity is that we have a magmatic intrusion at 3 to 9 km (1.8 – 5.6 miles) depth just west of Thorbjorn. It is most likely that this activity will stop without any volcanism," IMO stated.

On January 26, IMO reported unusually rapid inflation at Mt. Thorbjorn, indicating a possible magma accumulation.

Authorities have declared Uncertainty phase and raised the Aviation Color Code to Yellow. 

The fact that inflation is occurring alongside the earthquake swarm is a cause for concern and closer monitoring, IMO said.

"The inflation is unusually rapid, around 3 – 4 mm (0.11 – 0.15 inches) per day and has accumulated to 2 cm (0.78 inches) to date. It has been detected both on continuous GPS stations and in InSAR images," the office said, adding that the inflation is most likely a sign of magma accumulation at a depth of just a few km.

Images courtesy: IMO

Possible scenarios

The activity has only been ongoing for a few days and it is uncertain if it will escalate to more serious activity, IMO said last week.

Based on current information, the following scenarios are considered possible, without stating which is most likely or within what timeframe:

1. If the inflation is due to magma accumulation:

  • Magma accumulation will cease soon without further activity.
  • Magma accumulation continues for some time without further activity.
  • Magma accumulation will lead to a magma intrusion.
  • Magma accumulation will lead to magma intrusion and eruption (effusive fissure eruption).
  • Magma accumulation triggers seismic activity with larger earthquakes (up to M6.0).

2. If the inflation is not caused by magma accumulation:

  • The inflation might be linked to tectonic activity and lead to larger earthquakes (up to M6.0).

Geological summary

The Reykjanes volcanic system at the SW tip of the Reykjanes Peninsula, where the Mid-Atlantic Ridge rises above sea level, comprises a broad area of postglacial basaltic crater rows and small shield volcanoes.

The submarine Reykjaneshryggur volcanic system is contiguous with and is considered part of the Reykjanes volcanic system, which is the westernmost of a series of four closely-spaced en-echelon fissure systems that extend diagonally across the Reykjanes Peninsula.

Most of the subaerial part of the volcanic system (also known as the Reykjanes/Svartsengi volcanic system) is covered by Holocene lavas.

Subaerial eruptions have occurred in historical time during the 13th century at several locations on the NE-SW-trending fissure system, and numerous submarine eruptions at Reykjaneshryggur dating back to the 12th century have been observed during historical time, some of which have formed ephemeral islands.

Basaltic rocks of probable Holocene age have been recovered during dredging operations, and tephra deposits from earlier Holocene eruptions are preserved on the nearby Reykjanes Peninsula. (GVP)

Featured image credit: Google, TW

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