Rising Seismic Activity in Reykjanes: Two Likely Scenarios

Rising Seismic Activity in Reykjanes: Two Likely Scenarios

Ragnar Tómas

Daily earthquakes continue to increase in the Sundhnúkagígaröð area on the Reykjanes peninsula. According to the Icelandic Meteorological Office, sufficient pressure has built up in the volcanic system to potentially trigger a magma surge or an eruption in the coming days.

60 earthquakes over the past 24 hours

Around sixty earthquakes were recorded in the Sundhnúkagígaröð area on the Reykjanes peninsula – near the Svartsengi Power Plant – over the past 24 hours, compared to an average of 30 per day a little over a week ago, the Icelandic Meteorological Office has noted. Land uplift has slowed slightly.

These developments, along with increased seismic activity, indicate rising pressure in the volcanic system: “The question now is how much pressure the Earth’s crust can withstand before it gives way and a new magma intrusion begins,” the Icelandic MET Office noted in a statement.

The MET Office’s hazard assessment remains unchanged, as shown on the accompanying map.

“According to model calculations, the total volume of magma in the accumulation area under Svartsengi is now similar to before the eruption that began at the end of May. Initial model calculations projected that by the end of this week, the upper limit required to trigger a new magma intrusion and possibly an eruption would be reached. The rate of land uplift has slowed, suggesting that the timeline might extend further if no significant activity occurs in the coming days,” the MET Office notes.

Two likely scenarios

As noted by the MET Office, the following two scenarios are considered most likely:

Scenario 1:

An eruption with its origin between Stóra-Skógfell and Sundhnúkur (central part of area 3 on the hazard map). This location is similar to eruptions that began on December 18, 2023; February 8, March 16; and May 29, 2024.

• The likely precursor is a local swarm of small earthquakes between Stóra-Skógfell and Sýlingarfell, with acceleration in deformation and pressure changes in boreholes in the area.
• A very short warning period (less than 30 minutes).
• Lava could reach Grindavíkurvegur Road near Þorbjörn in under 1.5 hours and Grindavíkurvegur near the Svartsengi Power Plant outside the protective barriers in under 3 hours.

Scenario 2:

An eruption with its origin south of Sundhnúkur, at Hagafell or south of Hagafell (southernmost part of area 3 on the hazard map and upper part of area 4). This location is similar to the eruption that began on January 14, 2024.

• The likely precursor is a swarm of small earthquakes starting near Stóra-Skógfell or Sýlingarfell and moving south, with acceleration in deformation and pressure changes in boreholes in the area.
• The warning period for an eruption in this area is likely longer than in scenario 1, but it is uncertain by how much. The longer warning period depends on how far south the magma travels before reaching the surface.
• Lava could reach Nesvegur Road and Suðurstrandarvegur Road in under 1.5 hours. Lava flow could potentially block escape routes from Grindavík in about 6 hours.
• In this scenario, lava could reach the sea east of Grindavík in 1.5 to 3 hours. If lava reaches the sea, it could pose a localised hazard due to rapid cooling. Initially, the danger would be from ash and gas emissions, primarily hydrochloric acid (HCI). Conditions would be life-threatening within a 500-metre radius of where the lava contacts the sea.