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🌋 Iceland's Volcanoes: The Island Being Born

Understand why Iceland erupts so often — it sits on both a mid-ocean ridge and a hotspot, and the surplus melt built an island. You'll learn how eruptions from Laki to Eyjafjallajökull shaped history,

8
lessons
~45 min
to learn
🏛️ History
subject
Adults
level
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What you’ll learn

  1. An Island That Should Not Be Above WaterEstablish the course's question: not why Iceland has volcanoes, but why this stretch of mid-ocean ridge is above water at all.The Mid-Atlantic Ridge runs 65,000 km with its crest ~2.5 km underwater almost everywhere — except Iceland, where you can walk into the rift at Þingvellir. Iceland's spreading rate is unremarkable (18.9–20.2 mm/yr full rate by continuous GPS), but its crust is 20–40 km thick against a normal 7 km. The ridge here isn't being pulled apart faster; it's being fed roughly five times too much melt.
  2. Two Machines at One AddressExplain Iceland as two melt-producing machines at one address — and be honest about what is disputed.Ridges melt mantle by decompression; hotspots melt it by excess temperature. Iceland has both, and because melt production is highly sensitive to how far above the solidus you get, the effects multiply. Evidence for the hot anomaly: too-thick crust, the Greenland–Iceland–Faroe aseismic ridge as a track, and repeated eastward rift jumps. Whether a deep mantle plume exists is genuinely contested — a minority view attributes the anomaly to fertile recycled crust along the old Caledonian suture instead.
  3. Every Kind of Eruption, on One IslandUnderstand why Iceland produces both harmless lava rivers and continent-scale disruption — via silica, viscosity, and ice.Iceland's ~30 active volcanic systems are dominated not by cones but by fissures, because a spreading rift puts the crust in tension. Basalt (~50% silica) is runny and flows; rhyolite (~70%) is stiff, traps gas and explodes. Iceland has both because long-lived basaltic chambers in thick crust evolve toward silicic melts by fractional crystallisation. The third variable — ~11% of the island under ice — matters most for Iceland's history.
  4. Laki: What a Fissure Can DoGrasp the scale of the 1783–84 Laki eruption and separate its documented effects from the popular exaggerations.The 27-km Laki fissure erupted from June 1783 to February 1784, producing ~14–15 km³ of lava — the largest flow in recorded history — but killing nobody with lava. It released ~120 Mt of SO₂ and ~8 Mt of fluorine; fluorosis killed ~80% of Iceland's sheep, ~50% of cattle and horses, and the resulting famine (the Móðuharðindin) cut the population from 49,609 in 1783 to 40,381 by 1786. The haze reached Prague by 17 June and Britain by 23 June; European mortality effects are supported but still debated, and the largest popular claims outrun the evidence.
  5. Ice on Top of FireExplain how ice converts ordinary Icelandic eruptions into floods and continent-stopping ash.About 11% of Iceland is glaciated, and the ice sits on the volcanoes — Grímsvötn and Bárðarbunga under Vatnajökull, Katla under Mýrdalsjökull. Meltwater ponds under the ice and drains catastrophically as a jökulhlaup; the 1996 Gjálp flood peaked near 50,000 m³/s and destroyed part of the ring road, with no deaths because it was forecast. Water also shatters magma into very fine glass, which is why the small 2010 Eyjafjallajökull eruption closed 300+ airports and cancelled ~107,000 flights (~48% of air traffic, ~€1.3 bn to airlines per IATA).
  6. Heimaey: The Night They Fought the LavaSee the turn in Iceland's relationship with fire: the 1973 Heimaey eruption, where the lava was steered and the town came out ahead.A 1.6-km fissure opened beside Vestmannaeyjar town at 2 a.m. on 23 January 1973; a storm had brought the fishing fleet home, and ~5,300 people were evacuated by boat within hours with essentially no casualties. Lava buried ~400 houses and advanced on the harbour mouth, so Icelanders pumped seawater onto the flow front for five months — freezing its margin and deflecting it. The harbour survived and ended up better sheltered, and the cooling lava heated the town for years afterwards.
  7. Turning the Volcano into a UtilityUnderstand how Iceland converted volcanic heat into a national utility — and what the economics of unsellable energy produce.Shallow hot rock gives Iceland geothermal heat everywhere; district heating began with a Reykjavík school in 1930 and now heats roughly 90% of Icelandic homes, with essentially 100% renewable electricity (roughly 70% hydro, 30% geothermal). With no grid link to Europe and only ~390,000 people, the surplus must be exported embodied in products — hence aluminium smelters and, latterly, data centres, which is a live political argument. At Hellisheiði, CarbFix mineralises injected CO₂ into basalt, with over 95% turning to carbonate rock within about two years.
  8. Reykjanes: Watching It HappenFollow the live Reykjanes eruption episode, and see why the honest answer about its end is that nobody knows.Reykjanes erupts in multi-decade episodes separated by centuries of quiet; the last ended around 1240, and the next began at Fagradalsfjall in March 2021. In November 2023 a dike tore through Grindavík and its ~3,700 residents were evacuated overnight; nine eruptions occurred in the Sundhnúkur series between December 2023 and July 2025 (twelve since 2021). Earth barriers have repeatedly saved the Svartsengi power plant, and IMO inflation-based forecasts have worked days ahead — but how long the episode runs, and where it migrates, is unknown.

Questions this course answers

Why is 'Iceland sits on the Mid-Atlantic Ridge' an incomplete explanation of Iceland?

Every mid-ocean ridge has volcanoes — that's what a ridge is. The anomaly needing explanation is elevation: Iceland's crust is 20–40 km thick against a normal 7 km. The spreading rate (18.9–20.2 mm/yr) is if anything on the slow side. The ridge explains the eruptions; the surplus melt explains the island.

What is the honest state of the 'mantle plume under Iceland' claim?

The observable — excess melt, thick crust, the Greenland–Iceland–Faroe track, eastward rift jumps — is not in dispute. The cause is. Tomography sees a low-velocity anomaly but its depth extent is argued over, and a minority view attributes it to fertile recycled crust along the old Caledonian suture rather than a hot column. Textbooks that assert 'plume' flatly are ahead of the evidence.

Why is Iceland's dominant volcanic form a fissure rather than a cone?

It's a stress-field consequence. A rift is pulling apart, so cracks are open and available. Magma exploits them and erupts along a whole line at once — a curtain of fire — leaving a row of craters rather than a mountain. Iceland does have stratovolcanoes, but the fissure is what the ridge naturally produces.

Laki produced the largest lava flow in recorded history and the lava killed nobody. What actually caused a fifth of Iceland to die?

This is the chapter's whole point: basalt is the 'safe' magma and the lava was almost irrelevant. Fluorine deformed the teeth and bones of grazing animals — ~80% of sheep, ~50% of cattle and horses. In a 50,000-person subsistence economy that ran on sheep, that meant famine. The population fell from 49,609 (1783) to 40,381 (1786).

Which Laki claim should you treat with the most caution?

The haze chronology is documented across European records, the livestock and population figures come from Icelandic censuses, and the gas estimates are from petrological and ice-core work. The global death toll and revolution claims are extrapolations that run well past the evidence — 18th-century mortality had many drivers, and disentangling them is genuinely hard.

The 2010 Eyjafjallajökull eruption was small by volume. Why did it close European airspace?

Volume is the wrong metric. Water quenches magma and fragments it into fine, sharp glass shards, which stay airborne far longer than coarse ash. Glass melts in a jet engine and re-solidifies on the turbine blades. Add a jet stream aimed at Europe and you get ~107,000 flights cancelled and 300+ airports closed — from an eruption nobody would otherwise have heard of.

Grounded in trusted sources

  • H. Geirsson et al., 'Current plate movements across the Mid-Atlantic Ridge determined from 5 years of continuous GPS measurements in Iceland', JGR Solid Earth 111, B09407 (2006) — https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2005JB003717
  • Icelandic Meteorological Office (Veðurstofa Íslands) — volcano monitoring, deformation and eruption forecasts — https://en.vedur.is/
  • Global Volcanism Program, Smithsonian Institution — Icelandic volcanic systems — https://volcano.si.edu/
  • Wikipedia — Laki (eruption volume, 120 Mt SO₂, 8 Mt fluorine, livestock and population figures, European haze chronology) — https://en.wikipedia.org/wiki/Laki
  • 'More poison than words can describe: what did people die of after the 1783 Laki eruption in Iceland?', Natural Hazards and Earth System Sciences 24, 2971 (2024) — https://nhess.copernicus.org/articles/24/2971/2024/
  • Benjamin Franklin, 'Meteorological Imaginations and Conjectures' (Manchester Literary and Philosophical Society, 1784)
  • Wikipedia — Air travel disruption after the 2010 Eyjafjallajökull eruption (107,000 flights, 300+ airports, IATA €1.3 bn) — https://en.wikipedia.org/wiki/Air_travel_disruption_after_the_2010_Eyjafjallaj%C3%B6kull_eruption
  • USGS — Impact of the 2010 Eyjafjallajökull eruption on air routes — https://volcanoes.usgs.gov/volcanic_ash/ash_clouds_air_routes_eyjafjallajokull.html

Every Wunder lesson is built from real, reputable sources — never invented.

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