🌋VolcanoAtlas

Katla

Iceland's Most Feared Subglacial Volcano

Elevation

1,490 m

Last Eruption

1918

Type

Subglacial volcano (fissure vents)

Country

Iceland

Location

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Volcanic Hazards & Risk Assessment

Primary Hazards

  • Lava flows and fountaining
  • Volcanic gas emissions
  • Local explosive activity

Risk Level

Population at RiskHigh
Infrastructure RiskHigh
Aviation RiskSignificant

Geological Composition & Structure

Rock Types

Primary
Unknown
Silica Content
Varied composition

Tectonic Setting

Unknown
Intraplate setting with hotspot or regional volcanic activity.

Age & Formation

Epoch
Unknown
Evidence
Unknown

Eruption Statistics & Analysis

MetricValueGlobal RankingSignificance
Total Recorded EruptionsUnknownLowModerately active volcano
Maximum VEIVEI UnknownMinorLocal impact potential
Recent Activity108 years agoHistoricalHistorically active

Monitoring & Alert Status

Monitoring Networks

Global Volcanism Program
International eruption database

Current Status

Normal
No recent activity. Routine monitoring continues.

Authority Sources

Smithsonian GVP
Official volcano database

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a large ice cave with snow on the ground

Henrique Ferreira

via Unsplash

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Interesting Facts

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Katla's ~934 CE Eldgjá eruption produced approximately 18 km³ of basaltic lava — enough to cover the entire city of London to a depth of 12 meters and one of the largest lava flows in recorded human history.

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The current repose period of over 107 years since Katla's last eruption in 1918 is the longest in the volcano's documented history, leading Icelandic scientists to classify it as statistically overdue.

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During major eruptions, Katla's jökulhlaups can discharge water at 100,000–300,000 m³ per second — temporarily matching or exceeding the flow rate of the Amazon River.

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The 1918 eruption of Katla extended Iceland's southern coastline by up to 5 km in a single event, depositing an estimated 0.7 km³ of sediment on the Mýrdalssandur outwash plain.

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Three out of four historical eruptions of neighboring Eyjafjallajökull have been followed by eruptions of Katla, establishing a documented sympathetic volcanic relationship.

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Katla's tephra is characteristically rich in fluorine, making it highly toxic to grazing livestock — a property shared with the catastrophic 1783 Laki eruption that killed 50% of Iceland's livestock.

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The Mýrdalsjökull ice cap concealing Katla covers approximately 590 km² — roughly the size of the city of Chicago — and is up to 700 m (2,300 ft) thick.

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Katla's caldera measures 10 × 14 km and is up to 750 m deep, making it one of the largest calderas in Iceland, entirely hidden beneath glacial ice.

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The Eldgjá fissure system connected to Katla extends approximately 60 km to the northeast — longer than the distance from central London to Brighton.

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The Eldgjá eruption's sulfur dioxide emissions of an estimated 219 million tonnes may have contributed to the Christianization of Iceland by reinforcing apocalyptic interpretations of the cataclysm.

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Descriptions of fire and darkness in the medieval Icelandic poem Völuspá, part of the Poetic Edda, may record eyewitness observations of the ~934 CE Eldgjá eruption.

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The village of Vík í Mýrdal, Iceland's southernmost settlement with ~600 residents, conducts regular evacuation drills in preparation for the next Katla eruption, with warning time estimated at as little as 15–30 minutes.

Frequently Asked Questions

Is Katla volcano going to erupt?
Katla is considered very likely to erupt again, and Icelandic volcanologists regard it as statistically overdue. The volcano has erupted approximately 20–25 times since Iceland's settlement around 874 CE, at average intervals of 40–80 years. The current repose period of over 107 years since the 1918 eruption is the longest in documented history. The Icelandic Meteorological Office continuously monitors Katla using seismometers, GPS, satellite data, and river gauges. Periodic earthquake swarms and minor subglacial events (notably in 1999 and 2011) indicate an active magmatic system. While the exact timing cannot be predicted, scientists consider another eruption within coming decades a high probability.
When did Katla last erupt?
Katla's last confirmed eruption began on October 12, 1918, from the south side of its subglacial caldera. Rated VEI 4, the eruption lasted approximately three weeks and generated massive jökulhlaups (glacier-outburst floods) that reached the coast within 30 minutes, carrying blocks of glacier ice weighing thousands of tonnes. The floods deposited an estimated 0.7 km³ of sediment, extending Iceland's southern coastline by up to 5 km. Minor subglacial events in 1955 and 1999 are classified as uncertain eruptions, possibly involving small magma-ice interactions that did not break through the ice cap surface.
What would happen if Katla erupted today?
A major Katla eruption today would trigger catastrophic jökulhlaups with peak water discharge potentially exceeding 100,000 m³ per second, inundating the Mýrdalssandur and Sólheimasandur outwash plains. Bridges on Iceland's Route 1 ring road would likely be destroyed, temporarily severing the country's primary transportation link. The village of Vík í Mýrdal (~600 residents) would need to evacuate to higher ground with as little as 15–30 minutes' warning. Fluorine-rich tephra could poison livestock across southern Iceland. Volcanic ash in the atmosphere would likely disrupt transatlantic aviation, potentially on a scale comparable to or exceeding the 2010 Eyjafjallajökull crisis. Iceland's civil protection authorities maintain detailed contingency plans for this scenario.
What is a jökulhlaup?
A jökulhlaup (Icelandic for 'glacier run') is a catastrophic outburst flood caused when volcanic heat rapidly melts glacial ice. Katla is one of the world's most prolific producers of jökulhlaups due to the combination of its powerful subglacial eruptions and the vast Mýrdalsjökull ice cap above. During a major eruption, volcanic heat melts hundreds of millions of cubic meters of ice within hours. The resulting meltwater, mixed with volcanic debris and blocks of ice, bursts through the glacier's outlet glaciers and cascades across the outwash plains at enormous speed. Historical Katla jökulhlaups have reached peak flows of 100,000–300,000 m³/s — rivaling the world's largest rivers.
Is Katla connected to Eyjafjallajökull?
Katla and Eyjafjallajökull are neighboring volcanoes separated by approximately 25 km, and historical evidence suggests a sympathetic relationship between the two systems. Three of Eyjafjallajökull's four known historical eruptions (920, 1612, and 2010 CE) were followed by eruptions of Katla within months to years. Following the 2010 Eyjafjallajökull eruption that disrupted global aviation, there was significant concern that Katla might follow suit, though it has not erupted as of 2025. The two volcanoes are separate systems with distinct magma chambers, but they likely share deep crustal plumbing connections influenced by the same tectonic stresses.
How big was the Eldgjá eruption?
The Eldgjá eruption of approximately 934–940 CE was one of the largest volcanic events in recorded human history. Originating from Katla's northeastern fissure system, it produced roughly 18 km³ of basaltic lava and approximately 1.3 km³ of tephra along a fissure extending up to 75 km. The eruption's sulfur dioxide emissions — estimated at 219 million tonnes — rank among the highest of any historical eruption and caused measurable Northern Hemisphere cooling of approximately 0.7–1.0°C. The resulting Eldhraun lava field covers approximately 780 km² and remains one of Iceland's most striking geological features.
Can you visit Katla volcano?
The Katla caldera itself is inaccessible beneath hundreds of meters of glacial ice, but the surrounding region offers exceptional volcanic tourism. The Sólheimajökull outlet glacier, about 160 km from Reykjavík, provides guided glacier hikes and ice climbing experiences. Ice cave tours operate seasonally within Mýrdalsjökull's outlet glaciers. The Katla UNESCO Global Geopark encompasses the volcano and surrounding area. The Katla Exhibition Center in the village of Vík features interactive displays about the volcano's history and hazards. The Mýrdalssandur outwash plain and nearby Reynisfjara black sand beach showcase the dramatic volcanic landscape. Visitors should note that Katla could erupt with limited warning.
How does Katla compare to other Icelandic volcanoes?
Katla is one of Iceland's three most powerful volcanic systems alongside Grímsvötn and Bárðarbunga. With 131 documented eruptions, Katla has the second-highest eruption count in Iceland after Grímsvötn. Its VEI 5 capability exceeds that of most Icelandic volcanoes — only Öræfajökull (VEI 5) and Bárðarbunga (VEI 6) match or exceed it in maximum explosivity. Katla's Eldgjá fissure produced one of the largest known Holocene lava flows globally. Among Icelandic volcanoes, Katla poses the greatest jökulhlaup hazard due to the combination of its explosive power and the thick Mýrdalsjökull ice cap.