As the ice melted, the Earth's crust underwent isostatic rebound, a process where the reduction in pressure allowed magma to rise more easily to the surface, initiating volcanic activity.

However, the 2023 swarm was unusually extensive and is linked to a magmatic intrusion approximately 15 km (9.3 mi) long, extending south-west from Kálffellsheiði [ˈkʰaul̥ˌfɛlsˌheiːðɪ] and aligning with the Sundhnúksgígar crater chain, at a depth of 800 m (2,600 ft) at the shallowest point.

The creation of this graben-like formation on 10 November has enabled scientists to estimate the volume of the magmatic intrusion, which formed in a remarkably short period of six hours, as approximately 70 million m3 (2.5 billion cu ft).

[56] Supporting Benedikt's hypothesis, Freysteinn Sigmundsson from the University of Iceland, in February 2024, observed that minor seismic activity near Fagradalsfjall indicated potential magma movement, hinting at a possible eruption.

Magnús noted that while magma generally cools quickly, the surrounding rock stays hot and weak, maintaining a state of geological vulnerability in the area for several months, necessitating ongoing caution and monitoring.

[37] At the beginning of December 2023, recent GPS data from the Icelandic Meteorological Office (IMO) showed that the land had risen above its level prior to the start of the earthquake series in end of October 2023.

The first was seen to be moving in a westward direction towards the Blue Lagoon and the Svartsengi power plant and reached Route 43 (Grindavíkurvegur) leading into Grindavík, raising concerns that it could damage fiber optic cables laid on the road and cause internet and telecommunications disruptions.

[60][132] A recent study revealed that this eruption, along with all prior events in the series, has demonstrated "substantial mantle-derived geochemical variability" attributable to dynamic magma behavior in the mid-crust, thereby complicating efforts to predict future volcanic activity with accuracy.

[154][155] Two days after the May–June eruption began, sulfur dioxide levels in Edinburgh, Scotland spiked to 2,322 times higher than usual, the highest in about 50 years, due to strong North Atlantic winds.

[189] In response to the threat, fire crews were requested to the site and deployed an apparatus to apply water streams onto the lava flow, aiming to cool its surface, slow its progression, and protect the structural stability of the towers.

[226] While these measures offered substantial relief, property owners facing irreparable damage to their homes were obligated to allocate a segment of their insurance compensation—earmarked primarily for on-site repairs or reconstruction—to cover a disposal fee.

[242][243][244][245]As part of the government's comprehensive plan, which includes efforts by the Department of Civil Protection and Emergency Management to prevent freezing damages in houses and ensure that Grindavík remains functional and safe for future habitation,[246][247] up to 100 electricians and plumbers were mobilised to conduct critical repairs and upgrades, mostly from November 2023 to February 2024.

This initiative also involved essential infrastructure work to secure and maintain the electrical and plumbing connections between the town and the power station, especially in January 2024, when Grindavík's water main was engulfed by lava from the eruption.

[129][260][261][262] Approximately 120 to 150 residents commute to work in the town daily,[141] engaging in tasks such as discharging fishing vessels and conducting construction repairs on the harbor following the subsidence and earthquakes in November 2023.

[298][303][304] The Blue Lagoon is currently opened with operational hours subjected to adjustments based on forecasts of wind conditions and gas emissions, as well as any potential threats to nearby roads from volcanic activity.

[327] It was safely evacuated at the start of the 8 February 2024 eruption[328] but the hot springs were subsequently cut off by a fast-moving lava flow engulfing the northest stretch of Route 426 (Norðurljósavegur), its main access road.

[312][343] The chief of police stated that maintaining operations at the Blue Lagoon is scarcely justifiable amidst an ongoing eruption due to the risk of air pollution compromising public health.

Unlike conventional fire engine systems, these cannons were directly connected to excess water discharge from the Svartsengi power station, with a continuous supply potential of approximately 26,000 L/min (5,700 imp gal/min; 6,900 US gal/min).

This excess water, a byproduct of the power station that also formed the Blue Lagoon, was used in a system implemented in collaboration with multiple fire departments to effectively cool the lava, successfully stabilizing the flow and halting its progression.

[365] Simultaneously, an underground power cable was severely affected by the January 2024 eruption due to the immense heat and pressure exerted by the overlying lava, causing a temporary outage in half of the town.

[37] In early summer 2024, a new geothermal well was discovered through a collaborative project involving HS Orka, Iceland GeoSurvey, and the Department of Civil Protection and Emergency Management, under the leadership of the Ministry of the Environment, Energy, and Climate.

This initiative was launched following an emergency in February of the same year when the entire Suðurnes Peninsula lost all hot water for several days due to lava flowing over the main pipeline from the Svartsengi power station to the towns.

[392] During the November–December 2024 eruption, two transmission towers north of Svartsengi were at significant risk as lava drew closer to the protective filling at their bases, slowly approaching their concrete foundations and steel frames.

[384] Mitigation measures included deploying a fire truck to direct water jets onto the lava flow, with the goal of reducing its speed or altering its course to preserve the tower's structural stability.

Concerns grew as there was a chance the lava would make it to the ocean near the road, potentially causing minor explosions[426] and emitting toxic gases like hydrochloric acid (HCl) due to chemical reactions with the sea.

[429] Before the overspill, workers had already begun efforts to stop or slow down the lava by bulldozing old soil over it and using at least three firefighting trucks along with equipment from Keflavík Airport and Grindavík to pump water via fire hoses, with "quite good results".

[440][441][442] In the November–December 2024 eruption, lava advanced along the northern and north-western sides of Svartsengi's protective barriers, completely submerging the Blue Lagoon's entire parking area and the main section of the Route 426 (Norðurljósavegur) access road.

[459] On 20 March 2024, an incident at the Blue Lagoon resulted in an employee suffering from gas poisoning, attributed to a substantial release of sulfur dioxide from the March–May eruption in 2024, which was about 3 km (1.9 mi) from the geothermal spa.

[464] Birgir Jónsson, serving as CEO of Play Airlines at the time, claimed that extensive international media coverage of the volcanic eruptions in Grindavík caused substantial financial damage to Icelandic tourism, costing billions of krónas (tens of millions of dollars), in lost revenue.

[306][313] Jóhannes Þór Skúlason, Managing Director of the Icelandic Travel Industry Association, said the earthquakes and volcanic eruptions on the Reykjanes Peninsula negatively impacted tourist traffic during the holidays.