An update of recent geodetic observations and modelling results at key Icelandic volcanoes within the ISVOLC project

ISVOLC is a 12 partner research project funded by the Icelandic Research Fund, addressing the effects of climate change-induced ice retreat on seismic and volcanic activity. The project started 1 April 2023, and has a duration of 3 years. It is led by the Icelandic Meteorological Office, in collaboration with the University of Iceland.

Glaciers in Iceland have been retreating since 1890 and climate change simulations predict that the majority may disappear within a few hundred years. Retreating ice caps cause glacial isostatic adjustment (GIA) as well as changes to the subsurface stress field. Glacier covered volcanic systems are most affected, but also crustal conditions outside glaciers as well as magma generation at depth. Eruption likelihood may be modified, as occurred during the Pleistocene deglaciation, as more melt accumulates under Iceland because of ice retreat. However, there are several uncertainties: i) if, how and when this new magma reaches the surface; ii) if stability of existing magma bodies is modified; iii) if deglaciation is already resulting in accumulation of larger volumes of melt within crustal reservoirs; iv) how induced variations in the stress field may affect future volcanic activity. ISVOLC is focussing on four active volcanoes in Iceland (Katla, Askja, Grímsvötn and Bárðarbunga), to address these research questions.

Katla volcano lies beneath Mýrdalsjökull ice cap in S-Iceland. It is capable of generating large explosive eruptions within its caldera, with ash plume heights between 14-20 km accompanied by major jökulhlaups. GNSS observations from stations on nunataks of the glacier, and the surrounding region, combined with seismicity and changes to ice-cauldrons suggests a combination of processes are occurring, including GIA and magma inflow.

At Askja volcano, inflation commenced at end of July 2021 after decades of subsidence. This was detected on both GNSS observations and Sentinel-1 interferograms. Geodetic modelling indicates the onset of unrest was triggered by migration of magma within the uppermost part of the volcano plumbing system, followed by influx of new melt from depth. At the time of writing (January 2024) inflation continues but at a lower rate.

In the Bárðarbunga volcanic system, the six-month long 2014-2015 Holuhraun eruption was accompanied by gradual caldera collapse of up to 65 m and preceded by a two-week period of 48 km long lateral dyke propagation with extensive seismicity and deformation. Geodetic observations show that re-inflation started in July 2015, immediately after the end of the eruption. This may be explained by a combination of renewed magma inflow and viscoelastic readjustment of the volcano. GNSS and seismic observations show an increase in rate of inflation and seismicity since early 2023.

Grímsvötn subglacial volcano is the most frequently erupting volcano in Iceland, with eruptions in 1998, 2004 and 2011. A GNSS station shows a prominent inflation cycle between eruptions. Deformation at this volcano has surpassed that observed prior to recent eruptions and its aviation color code was elevated to yellow in January 2024 due to a short-lived intense seismic swarm.