Katla has erupted 18 times since 1245 — on average about once every 40 years. Yet its last confirmed eruption was in 1918. That's 108 years of silence, longer than any gap in its recorded history, from a volcano capable of unleashing a flood that briefly rivals the Amazon. Here's what the data says about Iceland's most closely watched sleeping giant — and how to stand on the glacier that hides it.
By VolcanoDB Research Team. Data: Smithsonian Global Volcanism Program (volcano #1436), Icelandic Meteorological Office, published jökulhlaup studies.
Last confirmed eruption
1918
Years since
108
Avg interval (since 1000 AD)
~40 yrs
Summit elevation
1,490 m
Katla in one paragraph
Katla is a large sub-glacial volcano in southern Iceland, hidden beneath the Mýrdalsjökull ice cap with a summit reaching 1,490 m. It sits inside a caldera about 10 km across and is one of the island's most powerful and frequently active systems — our database logs 18 confirmed eruptions since 1245. Its danger comes less from lava than from water: eruptions melt the overlying glacier and release jökulhlaups, catastrophic outburst floods. Katla has been quiet since 1918, and that unusually long pause is exactly why it's watched so closely.
Why Scientists Watch Katla So Closely
Start with the record. When you plot Katla's confirmed eruptions from our database entry, a rhythm appears: 18 eruptions between 1245 and 1918, spaced on average about 40 years apart since 1000 AD, and the longest gap in that entire span is 68 years. We are now 108 years past 1918. No other repose in Katla's written history comes close. That single fact is why "overdue" gets attached to Katla more than to almost any volcano on Earth.
A caution worth stating plainly, because most fear-driven articles skip it: volcanoes don't erupt on a schedule. An average interval is a description of the past, not a countdown timer. Magma supply, crustal stress and the weight of the ice cap all feed into the timing, and any of them can stretch or shorten the wait. What the statistics do justify is vigilance — which is why the Icelandic Meteorological Office runs a dense seismic, GPS and gas-monitoring network over Mýrdalsjökull and issues alerts on every notable earthquake swarm.
Katla also has a louder, deeper history than its 20th-century quiet suggests. The same volcanic system produced the Eldgjá eruption of 934–940 AD — a fissure event that poured out on the order of 18 cubic kilometres of lava, the largest basaltic flood eruption of the historic era, and one that spread a sulfur haze and cooling across the Northern Hemisphere. Katla, in other words, is capable of two very different modes: the explosive ice-covered eruptions of its recent record, and rare, enormous fissure outpourings like Eldgjá. Both matter when you think about a volcanic winter.
Katla Eruption History (from our database)
Every confirmed eruption below is drawn from the Smithsonian Global Volcanism Program record for Katla. Notice the tight clustering through the 1500s–1700s and the abrupt stop after 1918.
Year
VEI
What happened
1918
4
The last confirmed eruption. Triggered a jökulhlaup peaking above 300,000 m³/s and extended Iceland's south coast by up to 5 km.
1860
4
Sub-glacial explosive eruption from the south side of the caldera.
1823
3
Arcuate fissure eruption in the southern caldera.
1755
5
One of Katla's largest historic eruptions; catastrophic meltwater floods.
1721
5
Major explosive eruption with a large jökulhlaup.
1660
4
Explosive sub-glacial eruption.
1625
5
A powerful VEI 5 event — ash reached across southern Iceland.
1612
4
Followed closely on an Eyjafjallajökull eruption.
1580
4
Explosive sub-glacial eruption.
1500
4
Explosive eruption; part of a dense 15th–16th century cluster.
1416
4
Explosive eruption from beneath the ice cap.
1357
4
Eruption southwest of Kötlugjá.
1262
5
VEI 5 event in the same decade as the distant Samalas super-eruption.
1245
4
Earliest eruption individually catalogued in our database for Katla.
Table shows catalogued confirmed eruptions since 1245; Katla's full record includes additional older and uncertain events. For the complete list and coordinates, see the Katla database page.
1918: The Eruption Iceland Still Measures Against
In October 1918, Katla broke a 58-year silence. The eruption was graded VEI 4 and ranks among the largest in Iceland in the 20th century — but the numbers that stick are hydrological. The jökulhlaup that commenced on 12 October 1918 reached a calculated peak discharge of more than 300,000 cubic metres per second. For a few hours the flood plain of Mýrdalssandur carried more water than the Amazon. The total flood volume is estimated near 8 cubic kilometres of water, ice and sediment.
The land itself changed. The flood laid down roughly 0.7 cubic kilometres of sediment and pushed Iceland's southern coastline out by up to 5 kilometres in a single event — new land built by a volcano in a matter of days. Ash fell across the region and local farms were abandoned. Anyone modelling the next Katla eruption starts here, because 1918 is the benchmark for what the system can do to the coast, the Ring Road and the towns below.
What a Future Katla Eruption Would Actually Do
Katla is far more dangerous than its more famous neighbour precisely because it erupts under ice. Three hazards dominate:
Jökulhlaup (glacial outburst flood)
This is Katla's signature hazard, and the reason it's more dangerous than Eyjafjallajökull. When an eruption melts the base of the Mýrdalsjökull ice cap, a wall of meltwater, ice blocks and sediment bursts out in hours. The 1918 flood peaked at over 300,000 cubic metres per second — briefly rivalling the discharge of the Amazon — and dumped so much sediment it pushed the coastline out by up to 5 km.
Ash cloud and aviation disruption
Katla erupts through ice, and magma-meets-water eruptions fragment into fine, far-travelling ash. A 2010-scale event from Katla would likely be larger than Eyjafjallajökull's — the eruption that grounded 100,000 flights and stranded 10 million travellers across Europe.
Lightning, ballistics and coastal flooding
Explosive sub-glacial eruptions generate intense volcanic lightning and hurl ballistic blocks near the vent. Downstream, the flood plains of Mýrdalssandur and the Ring Road bridges are directly in the path of any outburst.
The Eyjafjallajökull Connection
Katla and Eyjafjallajökull are close neighbours with partly linked magma systems, and history shows them erupting in sequence — the smaller Eyjafjallajökull first, Katla soon after. That pattern appeared in 1612 and again around 1821–1823. So when Eyjafjallajökull erupted in 2010 and its ash cloud shut down European airspace — grounding roughly 100,000 flights — volcanologists braced for Katla to follow. It didn't. Whether 2010 broke the pattern or merely postponed the sequel is one of the open questions that keeps monitoring intense.
If Katla does go, most experts expect an eruption larger than Eyjafjallajökull's 2010 event — meaning a bigger ash cloud, a bigger jökulhlaup, and potentially far greater aviation disruption. You can track the wider picture on our Iceland volcano eruption guide, which covers all 44 Icelandic volcanoes and the ongoing Sundhnúkur / Svartsengi cycle on the Reykjanes Peninsula.
Visiting the Katla Area
You can't set foot on the active caldera, but you can stand on the glacier that hides it. The Katla region, based around the village of Vík on Iceland's south coast, is one of the country's best day-trip destinations from Reykjavík (about 2.5 hours by road).
Katla ice-cave tours — guided trips into the blue ice caves beneath Mýrdalsjökull, typically $130–190 per person and best from November to March. Super-jeep transport from Vík is usually included.
Glacier hikes on Mýrdalsjökull — crampon-and-ice-axe walks led by certified guides, roughly $90–150, available year-round for moderate fitness levels.
Vík and Reynisfjara — the black-sand beach, basalt sea stacks and puffin cliffs sit directly on the outwash plain a future jökulhlaup would cross.
Always check current Icelandic Met Office advisories before any glacier activity. Ice caves are natural and conditions change seasonally.
Frequently Asked Questions
Is Katla volcano going to erupt soon?
No one can predict the exact date, but Katla is clearly restless and statistically well past its typical repose. Our database records 18 confirmed eruptions since 1245, averaging roughly one every 40 years since 1000 AD — yet the last confirmed eruption was in 1918, 108 years ago. That's longer than any gap in its recorded history. Volcanoes don't erupt on a clock, so 'overdue' is a loose word, but the Icelandic Meteorological Office monitors Katla continuously precisely because a future eruption is considered a matter of when, not if.
What is a jökulhlaup and why does it make Katla so dangerous?
A jökulhlaup is a glacial outburst flood — a sudden torrent of meltwater released when a sub-glacial eruption melts the base of an ice cap. Because Katla sits under up to several hundred metres of Mýrdalsjökull ice, an eruption can unleash a catastrophic flood within hours. The 1918 jökulhlaup peaked above 300,000 m³/s and carried enough sediment to extend Iceland's southern coastline by about 5 km. The flood, not the lava, is the deadliest threat to the farms and roads below.
Can you visit Katla volcano?
You can't climb onto the active caldera — it's buried under the Mýrdalsjökull glacier — but the Katla area is one of Iceland's most popular tour regions. Guided Katla ice-cave tours run beneath the glacier (roughly $130–190, best from November to March), and glacier hikes on Mýrdalsjökull operate year-round. The base town of Vík, with the black-sand Reynisfjara beach, is about a 2.5-hour drive from Reykjavík along the south coast.
How is Katla connected to Eyjafjallajökull?
The two volcanoes are neighbours with linked plumbing, and historically Katla has often erupted within months or a few years of Eyjafjallajökull — in 1612 and around 1821–1823 the pair erupted in sequence. When Eyjafjallajökull produced its famous 2010 ash cloud, volcanologists watched Katla closely for a follow-on eruption. It hasn't come yet, which is one reason attention on Katla remains high.
When did Katla last erupt?
Katla's last confirmed eruption was in October 1918, a VEI 4 event that lasted about three weeks and produced a massive jökulhlaup. There were possible minor sub-glacial events in 1955 and 1999 that didn't break the surface as full eruptions. Counting from 1918, Katla has now been quiet for 108 years — its longest documented repose.