earth science

Sundhnúkur

Sundhnúkur is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sundhnúkur rather than just read about it. In short: Sundhnúkur (Icelandic pronunciation: [ˈsʏntˌn̥uːkʏr̥]) is a volcanic hill, within its associated Sundhnúksgígar crater row and volcanic fissures (Sundhnúksgígaröðin [ˈsʏntˌn̥uksˌciːɣaˌrœːðɪn]) in the Svartsengi volcanic system, part of the Reykjanes Peninsula rift zone of Iceland. It is the location of the 2023–2025 Sundhnúkur eruptions.

Key takeaways

Sundhnúkur belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sundhnúkur to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sundhnúkur from memory before moving on to harder problems.

Reference excerpt

Sundhnúkur (Icelandic pronunciation: [ˈsʏntˌn̥uːkʏr̥]) is a volcanic hill, within its associated Sundhnúksgígar crater row and volcanic fissures (Sundhnúksgígaröðin [ˈsʏntˌn̥uksˌciːɣaˌrœːðɪn]) in the Svartsengi volcanic system, part of the Reykjanes Peninsula rift zone of Iceland. It is the location of the 2023–2025 Sundhnúkur eruptions.

Geology The region has basalt lava shields with the larger ones being tholeiitic and smaller ones being picritic or tholeiitic. The hills are hyaloclastite table mountains or ridges and pillow lava mounds. The previous lava eruption from the Sundhnúkur crater row has been dated at 2350±90 BP, and was of basaltic ʻaʻā 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 8.3 km (5.2 mi) 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 or Svartsengi volcanic system which is part of the Reykjanes volcanic belt. 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 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 4 km (2.5 mi) north-east of Grindavík, and noted that the eruption stemmed from a fissure with a length of about 3.5 km (2.2 mi), 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 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, 42 km (26 mi) away. By 19 December, the scent of smoke and ash was detected as far as 30 km (19 mi) from the eruption site, raising fears that volcanic gases could reach Reykjavík by the next day.

Further eruptions

The eruptions continued into 2024. An eruption started on 14 January 2024, lasting two days, with property damage, including to the town of Grindavík. The next eruption commenced on 8 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 stopping at the start on the 16 March eruption. The eruption finished on 9 May. In the interlude between the 16 March and 29 May 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 1 June 2024 due to contact with groundwater that has accumulated from rain. The amount of available magma was estimated to be around 20 million cubic metres. The fifth eruption ceased on 22 June and afterward inflow continued into the magma reservoir. At 21:26 UTC on 22 August a fissure erupted to the north of the previous eruptions, in what transpired by the time it ended on 5 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 20 November and 9 December 2024. The 8th brief eruption commenced just before 9:45 UTC 1 April 2025, lasted 6 hours and covered about 0.23 km2 (0.089 sq mi) to an average thickness of 1.7 m (5 ft 7 in) in lava. The 9th eruption commenced on 16 July 2025 at 3:54 UTC, and finished on the 4 August 2025.

See also Geography of Iceland Southern Peninsula (Iceland) Geology of Iceland Geology of Reykjanes Peninsula Volcanism of Iceland

References

Illustrations

Worked examples

Example 1 — a first encounter with Sundhnúkur

Start with the simplest possible case. Write down what Sundhnúkur claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sundhnúkur before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sundhnúkur ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sundhnúkur

In research: Sundhnúkur appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sundhnúkur in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sundhnúkur is common in secondary-school and first-year university syllabi. It links to neighbouring topics Active volcanoes, Fissure vents, Reykjanes Volcanic Belt, so understanding it makes those chapters shorter.
In everyday life: Look for Sundhnúkur outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sundhnúkur in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sundhnúkur means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sundhnúkur out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sundhnúkur in simple terms?

Why does Sundhnúkur matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sundhnúkur?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sundhnúkur.