The Aviation Color Code for Grímsvötn volcano was raised from Green to Yellow on September 30, 2020. The last eruption of this volcano took place in 2011 -- it was a large and powerful VEI 4 eruption. The average eruption frequency during the last 1 100 years is 1 eruption per 10 years.
According to the Icelandic Met Office, the volcanic activity at the volcano has been gradually increasing over time as indicated by several regularly monitored geophysical and geochemical parameters that are now above the known background level:
- The seismicity during the past month has been above average
- Geothermal activity has increased over the past months with clear signs of deepening cauldrons in several places around the caldera
- The surface deformation has exceeded the level it was at prior to the 2011 eruption
- Magmatic gases were measured in the geothermal emissions this summer.
"In addition, the water height in the subglacial lake is comparable to the level prior to the floods in 2004 and 2010, increasing the likelihood of a flood in the coming months," IMO said in a statement released today.
"Multiple datasets now indicate that Grímsvötn volcano has reached a level of unrest, comparable to that observed prior to historic eruptions," it added.
Aviation Color Code Yellow does not mean that an eruption is imminent.
However, an eruption could be triggered by depressurization if the subglacial lake inside the caldera will drain and cause a flood or occur regardless, possibly with very weak precursory activity and short warning time, as seen in the eruption of 2011.
Image credit: IMO
The conditions at the volcano may change at any given time and the volcano may return to normal background conditions without further escalation, IMO volcanologists said.
Because the Civil Protection meets regularly with IMO and is informed about the situation, there are currently no reasons to change the alert level of civil protection.
On June 15, 2020, IMO announced Grímsvötn volcano is showing strong signs that an eruption might occur in the weeks or months ahead.
According to Melissa Anne Pfeffer, IMO's atmospheric volcanologist, high levels of magmatic gasses were present at the time in the southwest corner of the volcano, near the place where it erupted in 2004 and 2011.
"This is the first time that we measure so much SO2 at a volcano in Iceland that is not in an eruptive phase and its presence is indicative of magma at a shallow level," Pfeffer said in June 2020.
In addition, the volcano was experiencing inflation, indicating an increase in magma.
Grímsvötn's last eruption started at approximately 17:30 UTC on May 21, 2011, with a plume of volcanic ash and steam rising to about 20 kilometers (65 600 feet) above sea level. Overnight, the plume height dropped to 15 kilometers (49 000 feet), but occasionally re-approached the initial altitude.
Ash from the volcano reduced visibility to about 50 meters (160 feet) in some places and made some areas as dark as night in the middle of the day. The ash plume also prompted the closure of Keflavik, Iceland’s largest airport.
In the past years, the Aviation Color Code has been changed several times for a few volcanoes in Iceland. The most recent ones have been for Reykjanes in January 2020, Öræfajökull in 2017, Katla in 2016, and Bárðarbunga in 2014-2015 in connection to the Holuhraun eruption.
The Aviation Color Code has been raised to orange/red on several occasions, with the most recent case during the last eruption in Bárðarbunga.
Grímsvötn, Iceland's most frequently active volcano in historical time, lies largely beneath the vast Vatnajökull icecap. The caldera lake is covered by a 200 m (650 feet) ice shelf, and only the southern rim of the 6 x 8 km (3.7 x 5 miles) caldera is exposed.
The geothermal area in the caldera causes frequent jökulhlaups (glacier outburst floods) when melting raises the water level high enough to lift its ice dam.
Long NE-SW-trending fissure systems extend from the central volcano. The most prominent of these is the noted Laki (Skaftar) fissure, which extends to the SW and produced the world's largest known historical lava flow during an eruption in 1783.
The 15 km3 (3.6 mi3) basaltic Laki lavas were erupted over a 7-month period from a 27 km (16.7 miles) long fissure system. Extensive crop damage and livestock losses caused a severe famine that resulted in the loss of one-fifth of the population of Iceland.
Featured image credit: IMO