Sundhnúkur () is a volcanic hill, within its associated

Sundhnúksgígar Sundhnúksgígar () or Sundhnúkagígar is a series of volcanic craters east of Eldvörp–Svartsengi in Iceland. They are named after Sundhnúkur, which is a hill just south of Sundhnúksgígar. The craters are aligned in a row called ''Sundhn ...

crater row and volcanic fissures ( ) in the Svartsengi volcanic system, part of the

Reykjanes Peninsula Southern Peninsula (, ) is an administrative unit and part of Reykjanesskagi (pronounced ), or Reykjanes Peninsula, a region in southwest Iceland. It was named after Reykjanes, the southwestern tip of Reykjanesskagi. The region has a populatio ...

rift zone A rift zone is a feature of some volcanoes, especially shield volcanoes, in which a set of linear cracks (or rifts) develops in a volcanic edifice, typically forming into two or three well-defined regions along the flanks of the vent. Believed ...

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

. It is the location of the

2023–2025 Sundhnúkur eruptions The 2023–2025 Sundhnúkur eruptions () are a series of volcanic eruptions on the Southern Peninsula (Iceland), Reykjanes Peninsula, near the town of Grindavík, Iceland. Between December 2023 and April 2025, there have been eight eruptions, fo ...

Geology

The region has

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

lava shields with the larger ones being

tholeiitic The tholeiitic magma series () is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic ...

and smaller ones being picritic or tholeiitic. The hills are

hyaloclastite Hyaloclastite is a volcanoclastic accumulation or breccia consisting of glass (from the Greek ''hyalus'') fragments (clasts) formed by quench fragmentation of lava flow surfaces during submarine or subglacial extrusion. It occurs as thin marg ...

table mountains or ridges and

pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or ''subaqueous extrusion''. Pillow lavas in volcanic rock are characterized by thick sequences of discontinu ...

mounds. The previous lava eruption from the Sundhnúkur crater row has been dated at , and was of basaltic aā type. The lava field that erupted prior to 2023 extends north-east from Grindavík in the south with the fissures and Sundhnúksgígar crater row extending at strike of 35°. This takes the fissure system past the older mountains of Hagafell to its east and Svartsengisfell to its west. The crater row is usually now classified as part of the

Eldvörp–Svartsengi Eldvörp–Svartsengi (); "fire cones–black meadow" in Icelandic also Svartsengi volcanic system) is a volcanic system in the southwest of Iceland on the Southern Peninsula, southeast of Keflavík International Airport and north of the town of ...

or Svartsengi volcanic system which is part of the

Reykjanes volcanic belt The Reykjanes Peninsula ( ) in southwest Iceland is the continuation of the mostly submarine Reykjanes Ridge, a part of the Mid-Atlantic Ridge, on land and reaching from Esjan, Esja in the north and Hengill in the east to Reykjanestá in the ...

. There are previous classifications that included the volcano in the Reykjanes volcanic system and what was termed the Grindavik volcanic fissure system.

18 December 2023 eruption

On the evening of 18 December 2023, a volcanic eruption occurred at Sundhnúksgígaröð north of Grindavík, with images showing lava spewing from

fissures A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes. Ground fissure A ...

in the ground. The intensity of the eruption and accompanying seismic activity which preceded it decreased early on 19 December, with lava seen spreading laterally from both sides of the newly opened fissures. Iceland's Meteorological Office said the eruption occurred at around 22:17 GMT following a series of small earthquakes at around 21:00. It pinpointed the origin of the eruption near Hagafell, about north-east of Grindavík, and noted that the eruption stemmed from a fissure with a length of about , with lava flowing at a rate of around 100 to 200 cubic metres per second, adding that seismic activity appeared to be moving towards the direction of Grindavík. An Icelandic Civil Defence official told the public broadcaster

RÚV Ríkisútvarpið (, ; abbr. RÚV ) is Iceland's national public broadcasting, public-service broadcasting organization. Founded in 1930, it operates from studios in the country's capital, Reykjavík, as well as regional centres around the count ...

that the eruption had happened quickly and appeared to be "quite a large event". The eruption was described as the largest in the area since the beginning of activity in 2021, and was visible as far away as the capital

Reykjavík Reykjavík is the Capital city, capital and largest city in Iceland. It is located in southwestern Iceland on the southern shore of Faxaflói, the Faxaflói Bay. With a latitude of 64°08′ N, the city is List of northernmost items, the worl ...

, away. By 19 December, the scent of smoke and ash was detected as far as from the eruption site, raising fears that

volcanic gas Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities (Vesicular texture, vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from ...

es could reach Reykjavík by the next day.

Further eruptions

The eruptions continued into 2024. An eruption started on 14th January 2024, lasting two days, with property damage, including to the town of

Grindavík Grindavík () is a fishing town in the Southern Peninsula district of Iceland, not far from Þorbjörn, a tuya (a type of flat-topped, steep-sided volcano). It is one of the few towns with a harbour on this coast. Most of the inhabitants work ...

. The next eruption commenced on the 8th February 2024, and finished the next day with road and hot water supply infrastructure damage. Another eruption began on 16 March 2024 that lasted for an unusually long period of time. The eruption was initially a row of fissures, but has since then been confined to 1 crater. As of 25 April 2024, land uplift resumed after almost grinding to a complete halt at the start on the March 16 eruption. The eruption finished on the 9th of May. In the interlude between the March 16 and May 29 eruptions, land uplift occurred. At 12:45:58 UTC on 29 May, the fissure had its fifth eruption that petered out (but did not completely stop) over the course of 24 hours. Its fifth eruption has been the one of this sequence with the most volcanic ash released as of June 1, 2024 due to contact with groundwater that has accumulated from rain. The amount of available magma is estimated to be around 20 million cubic metres. The fifth eruption ceased on 22nd June and afterward inflow continued into the magma reservoir. At 21:26 UTC on the 22nd of August a fissure erupted to the north of the previous eruptions, in what transpired by the time it ended on 5th September, to be the largest eruption of the series, with lava subsequently spreading over an area known to have old American munitions. The second largest eruption of the series occurred between 20th of November and 9th of December 2024. The 8th eruption commenced just before 9:45 UTC 1 April 2025.

References

{{DEFAULTSORT:Sundhnúkur Active volcanoes Fissure vents Subglacial volcanoes of Iceland Volcanic fields Volcanism of Iceland Reykjanes Volcanic Belt

Geology

18 December 2023 eruption

Further eruptions

See also

References