Volcanoes
Katla Volcano: The sleeping giant of Iceland
Katla, one of Iceland's most formidable and recognizable volcanoes, looms beneath the Mýrdalsjökull glacier in southern Iceland. Its name evokes awe, as Katla’s eruptions have historically sometimes been cataclysmic, reshaping landscapes and lives. In this article, we explore Katla’s geological characteristics, its storied history, the notorious 1918 eruption, and the risks it poses today.
Katla's significance for Lava Show
Katla has special significance for us at Lava Show. The lava melted at our shows in Vík, and Reykjavik come from the 1918 eruption of this powerful volcano. Furthermore, at the show in Vík, we tell the story of how our founder's great great grandfather narrowly escaped from perishing in the 1918 eruption.
Key geological and geographical highlights of Katla volcano
*Remember, a glossary of geology terms sits here.
Type: Subglacial stratovolcano, tuya morphology.
Caldera: Measures approximately 10 kilometers (6+ miles) in diameter, covered by a thick ice cap.
Activity: Erupted at least 20 times since Iceland’s settlement in the ninth century
Eruption Style: Predominantly explosive eruptions, but occasional large-scale, fissure-style effusive eruptions, both of which can produce massive jökulhlaups (glacial outburst floods) as heat from eruptions melts the overlying ice.
Tephra Deposits: Katla’s basaltic and rare silicate tephra layers are widely dispersed, with some reaching as far as mainland Europe.
Location: Under Mýrdalsjökull glacier, about 20 km due north of Vík and 180 km southeast of Reykjavík.
Map of earthquakes recorded at Katla volcano in 2025, monitored by the Icelandic Meteorological Office, showing seismic activity beneath Mýrdalsjökull glacier.
Katla, the more active, big sister to the globally infamous Eyjafjallajökull, is perhaps mischaracterized as being dormant. While this volcano has not explosively erupted in modern times (i.e., recent decades), it is far more historically active and havoc-wreaking than its air traffic-stopping neighbor, Eyjafjallajökull. In fact, given its position under a thick glacier, it is quite possible that many smaller eruptions have occurred with limited detection, including three such possible events since 1950. In the absence of modern measurements and constant observation, historical records primarily chart the volcano’s explosive history only. But Katla has a dramatic, deep history for hundreds of thousands of years.
Before Time: Prehistoric Eruptions
Born over 800,000 years ago, most of Katla’s eruptive history, as captured in Iceland’s rock record, was eroded away during the last glacial Ice Age, approximately 10,000 years ago. Even in the absence of written record, scientists can track eruptive past through the mapping of ash and tephra layers throughout Iceland and in neighboring continents. Katla’s prehistoric activity is marked by large eruptions, some of which significantly influenced global climates:
~6,600 BC: Evidence from sediment cores indicates a major eruption, with ash deposits found across the North Atlantic region.
~2,900 BC: A large eruption left substantial tephra deposits in Greenland ice cores, suggesting widespread impact.
~1,500 BC: Katla’s activity during this period is associated with severe climatic cooling, as recorded in European tree rings and Arctic ice.
These ancient eruptions underscore Katla’s potential for widespread impact in Iceland and beyond. If you are interested in what the south Iceland region could look like directly after a large-scale, tephra-rich eruption, the series Katla on Netflix shows the town of Vík and the surrounding dried river flood plains blanketed in meters of ash and sand.
Beyond this, the effusive eruptions associated with Katla should not be understated. Three massive fissure eruptions have been noted in the rock record at Katla, the last being right after Iceland’s settlement in the year 939 with the onset of the Eldgjá eruption. These are like the eruptions at Fagradalsfjall and Sundhnúkur on the Reykjanes peninsula, but with an exponentially larger length and output. This eruption, called Eldgjá along with the canyon the lavas now inhabit, created the longest series of fissures ever recorded in Iceland at almost 80 km (50 miles) in length, and was the largest effusive eruption of the last millennia in terms of erupted lava volume. The area of lava that was deposited from these fissures during the almost year-long eruption would be equal to the entire metropolitan capital area of Reykjavík and its suburbs. This eruption also has associated tephra found in Greenland due to an initial preatomagmatic (i.e., ice-magma interaction) explosion, and ejected gases and aerosols into the atmosphere that impacted global climate for years.
Katla’s powerful 1918 eruption sent a towering ash cloud into the sky, marking one of Iceland’s most significant volcanic events of the 20th century.
Katla eruptions in the modern historical record
Since the settlement of Iceland in the ninth century, Katla has produced over 20 notable explosive eruptions, including Eldgjá mentioned above. Four of those eruptions were rated VEI-5; one of those eruptions notably resulted in two deaths from lightning that formed from the resulting towering ash cloud. The 1918 eruption of Katla is one of its most infamous events, still fresh in the cultural consciousness, remembered for its power and consequences. Given that first-hand accounts of this eruption indicate people in Vík were anxious that preceding seismic events were signs that Katla was waking up indicates that this volcano has been in the cultural historical memory for centuries.
Timeline: began on October 12, 1918, lasting approximately 24 days.
Precursors: felt and perceived seismicity around Vík a few hours before the eruption
Explosivity: classified as a VEI-4 event; one of the largest eruptions in Iceland’s 20th century.
Glacial outburst - Jökulhlaup: catastrophic glacial flooding, releasing an estimated 8 km³ (2 mi³) of meltwater; carried massive icebergs and sediment, reshaping the Mýrdalssandur plains and extending Iceland’s coastline by up to 5 kilometers in some areas.
Tephra and Ashfall: ash clouds darkened the skies with frequent lightning, with deposits recorded throughout Iceland and as far away as mainland Europe; fallout severely impacted agriculture by contaminating water sources and blanketing farmlands.
Environmental Impact: significant sulfur dioxide released, contributing to regional climatic anomalies.
Human Impact: no fatalities were directly attributed to the eruption, though destruction of farmlands and infrastructure caused hardships for local communities.
Icebergs left behind after the devastating glacial outburst flood (jökulhlaup) that followed Katla’s 1918 eruption. For scale, notice the man on the right.
Flooding did not just end with the initial eruption, but continued in punctuated pulses throughout the almost month-long event. Icebergs that were deposited onto the flood plains by floods were so large they stayed there for months, and an ice canyon 1700 m long x 500 m wide x 130 m deep was carved into the glacier from the initial flood outburst. The fast-moving, widespread nature of these floods means they are sometimes the most dangerous, life-threatening part of these large, explosive eruptions.
Regarding the eruption itself, tephra fall, primarily ash, was noted as falling somewhere within Iceland daily during the eruption. Later mapping revealed that an area of 20,000 m2 received a tephra layer of 0.5 cm or greater (for comparison, the capital metropolitan area in Iceland is just under 800 m2). Like the flooding, tephra fall also came in perceptible pulses, with the longest lasting thirteen straight hours and depositing 3-4 cm of ash nearby.
Extra Saga: Katla’s link to Lava Show
The story of Katla is told in the Lava Show showroom in the town of Vík. In 1918, the great-grandfather of our co-founder, Júlíus (the original Mr. Lava Lava), was a part of a group of men herding sheep on horseback on Mýrdalssandur (glacial flood plain). They first heard a low rumbling and the loud booming sounds.
When they saw a wall of water coming towards them at speed, some 2-3 meters high, they were forced to gallop to the nearest hill, barely escaping with their lives. Unfortunately, their livestock did not survive. Other first-hand accounts discuss how house-sized icebergs were deposited in people’s yards at their farms, and how the nights were fully blacked out, save for frequent lighting, as so much tephra and ash was falling.
The 1918 eruption serves as a stark reminder of Katla’s destructive potential, particularly its ability to unleash sudden, large-scale floods and widespread ash fall.
Modern Eruption Evidence and the Next Big Eruption
Since the 1918 eruption, there have been no explosive, above-ice eruptions at Katla. However, there have been multiple unconfirmed, subglacial events associated with evidence that a heat-producing episode had occurred. In 2011, more than a year after the eruption of Eyjafjallajökull, geophysical signals consistent with subsurface magma movement were measured, followed by a destructive jökulhlaup. This outburst flood destroyed a bridge along the Ring Road during high tourist season, leaving travelersand entire towns stranded and cut-off from resources.
In the months leading up to the event, inflation (ground rise) was recorded at GPS stations across the glacier that covers Katla. Weeks before the flood, a harmonic tremor was recorded. This low-frequency, longer-duration acoustic signal is a primary, tell-tale sign of magma ascending. This was followed by a very shallow earthquake swarm. These key indicators, combined with the glacial outburst flood, lead geologists to believe a minor eruption or hydrothermal/geothermal event took place. Without tangible evidence of an eruption (lava, ejecta, tephra, ash cloud), these events' origins remain unclear.
This leads scientists and locals to ponder when the next big Katla eruption will occur, and if there will be warning signs. Anecdotally, the hypothesis that Katla always erupts after Eyjafjallajökull seems to be a case of “correlation is not necessarily causation.” With only four Eyjafjallajökull eruption data points since written history began in Iceland, at least 16 Katla eruptions not linked to any other volcanic activity, and an unconfirmed Katla eruption subsequent to the large 2010 headline-making eruption, this trend cannot be confirmed. Additionally, summer “warmth” here in Iceland causes an uptick in shallow seismic activity related to shifting and melting ice, as well as smaller jökulhlaups, which can cloud underlying magmatic signals. For example, 390 earthquakes have occurred at Mýrdalsjökull since the beginning of this year, but 314 of those have occurred since May 1st.
With this in mind, it seems the clearest precursor signs to be:
Summit inflation (ground rise) - months to weeks ahead of eruption
Earthquake swarms - some months to weeks before, larger episodes hours before
Harmonic tremors - most likely weeks to days prior
Melting caldera ice - if seen, months to weeks in the lead-up
Sulfur smell or steam - if it occurs, just hours preceding
Given that Katla has not erupted since the advent of modern measurement and observation technology, there is no clear set of precursor data that exists yet. Scientists rely on analogs and anecdotal evidence to formulate hypotheses on what will happen at Katla in the lead-up to an eruption.
Of course, the question on everyone’s mind is when will Katla erupt next? This is, obviously, not easy to answer. Currently, there are no geophysical signs that indicate Katla is preparing to erupt, but eruption trends would indicate that sometime (geologically) soon a large eruption will occur. Looking at Katla statistics, the average time between eruptions is anywhere from 20-90 years, with a mean of 48 years. Thus, the 107 years between now and 1918 is 1.34 standard deviations above the mean, and explosive eruptions at Katla have a 92% probability of happening by now. There is, however, no telling if that next big eruption will be next month or in 50 years, and volcanoes erupt whenever they want.
Mýrdalsjökull glacier, under which the mighty Katla volcano lies dormant, shaping Iceland’s dramatic landscapes.
Katla’s Risk Today
So why worry about a Katla eruption? Katla’s dormancy since 1918 has heightened concerns about the potential for a large-scale eruption, given the time that has elapsed to accumulate magma. After seeing what happened with explosive eruptions at next-door Eyjafjallajökull in 2010 and regionally adjacent Grimsvötn in 2011, current risks can include:
Seismic Activity: Increased earthquake swarms under Mýrdalsjökull can cause earthquakes that dislodge ice before powerful flooding and can be felt regionally and at local tourist attractions along and atop the glacier.
Ice Melt and Flooding: An eruption could rapidly melt large volumes of glacial ice, producing catastrophic jökulhlaups that threaten nearby communities and infrastructure, including Route 1, Iceland’s main highway, and the village of Vík.
Air Travel Disruption: Ash plumes from a Katla eruption could impact transatlantic flight routes, as seen during the 2010 and 2011 eruptions.
Climate Impact: Katla’s potential to release sulfur dioxide could lead to short-term climatic cooling, with effects felt globally.
Preparedness & Resources: Iceland is incredibly prepared and trained for eruptive events, but since it is a small island nation, personnel and resources are finite and can put strain on rescue, government, and law enforcement organizations; the addition of travelers who are not as familiar with volcano safety and warning signs as locals adds an unpredictable element to evacuations and cordoning.
Volume of Lava and Tephra Generated by Katla
Katla’s eruptions are remarkable for the immense volumes of lava and tephra they produce:
Lava: While Katla’s eruptions are primarily explosive, some events have produced substantial lava flows. The 1918 eruption alone generated significant lava deposits that reshaped the local landscape.
Tephra: Katla’s tephra production is among the largest of Icelandic volcanoes. Estimates suggest some eruptions have released over 2 cubic kilometers (0.48 cubic miles) of tephra, with layers found across Europe and Greenland.
Jökulhlaup Sediment: The floods resulting from eruptions transport vast amounts of glacial sediment, further transforming the surrounding plains.
This prolific output underscores Katla’s power, contributing both to its local hazards and its far-reaching geological impact.
Comparisons to Well-Known Volcanoes Around the World
To understand the scope of Iceland's volcanics and Katla's place within that context, a look at global volcanic statistics to set the scene can help. Of the 203 VEI-4 or larger volcanic eruptions that happened around the world from 1600 onward, 31 of them happened outside of the Pacific Ring of Fire. Subduction settings like this dominate the global volcanic landscape, and on average, produce far larger and more numerous eruptions than other geologic settings. That said, of the 31 eruptions beyond the Pacific Rim, 22 of those happened in Iceland. Iceland´s volcanoes are the most prolific non-subduction* systems in the world. And of those 22, a staggering eight can be attributed to Katla.
*above the ocean
To further provide context, Katla’s activity can be compared to several famous volcanoes, highlighting its unique characteristics:
Vesuvius (Italy): Both Katla and Vesuvius are capable of producing explosive eruptions. The famous 79 AD eruption was a VEI-5, producing a deadly pyroclastic flow and scorching ash fall, and previous eruptions prehistoric are hypothesized at VEI-6. However, Katla’s jökulhlaups add a dimension of flooding not seen with Vesuvius.
St. Helens (USA): Katla’s eruptions rival Mount St. Helens in explosivity, with the 1980 eruption labeled at VEI-5, too. But, again, Katla’s subglacial setting increases the risk of massive floods.
Pinatubo (Philippines): the largest volcanic eruption of the last 100 years, this VEI-6 eruption lasted on and off for over a year, and, similar to the above-listed volcanoes, produced deadly pyroclastic flows. Katla produced smaller ash clouds, and eruptions are usually of shorter duration than Pinatubo.
Krakatoa (Indonesia): Known as the loudest explosion ever recorded by man, this VEI-6 eruption caused a five-year-long volcanic winter and destroyed entire islands. Both volcanoes can generate global climatic effects through ash and gas emissions, though Katla’s eruptions are often less frequent and usually not on the same scale.
Eyjafjallajökull (Iceland): Katla’s eruptions are typically larger and more destructive, with greater volumes of tephra and more extensive flooding. So everything experienced in 2010 could be much more widespread and effective with a Katla eruption.
Reykjanes (Iceland): These eruptions are almost all primarily fissure style eruptions, with only very small preatomagmatic explosions that happen with groundwater. Katla has occurrences of effusive fissure eruptions like those seen on Reykjanes, like at Fagradalsfjall and Sundhnúkur, but on a much larger, longer, and deadlier scale.
Katla’s unique combination of explosive power, gas emissions, glacial flooding, and widespread ashfall makes it one of the most hazardous volcanoes in Iceland, but also regionally and globally with atmospheric and climatic effects. While Katla is not “overdue” nor “sleeping” as discussed, as each year passes, Katla grows more primed to erupt again. A stop at the Lava Show in Reykjavík or Vík will help prepare you with information and awe about the possibilities that Katla possesses.
Frequently Asked Questions About Katla Volcano
Where is Katla volcano?
Katla lies beneath the Mýrdalsjökull glacier in South Iceland, approximately 20 kilometres north of Vík and 180 kilometres southeast of Reykjavík.
What type of volcano is Katla?
Katla is a large subglacial volcano with a caldera approximately 10 kilometres across. Its volcanic system can produce both explosive eruptions and enormous effusive fissure eruptions.
Why is Katla called Iceland’s “sleeping giant”?
Katla is called a sleeping giant because it is one of Iceland’s most powerful volcanoes but has not produced a confirmed major eruption since 1918. However, “sleeping” does not mean inactive: scientists continue to detect earthquakes, geothermal activity and other signs of unrest around the volcano.
How often has Katla erupted?
Katla has erupted at least 20 times since Iceland was settled in the ninth century. Geological evidence also reveals a much longer eruptive history extending back hundreds of thousands of years.
When did Katla last erupt?
Katla’s last confirmed major eruption began on 12 October 1918 and lasted approximately 24 days. Possible smaller subglacial events may have occurred since then, but these have not been conclusively confirmed as eruptions.
What happened during Katla’s 1918 eruption?
The VEI-4 eruption produced a towering ash cloud, widespread tephra fall and a catastrophic glacial outburst flood. The flood transported enormous icebergs and volumes of sediment across Mýrdalssandur, dramatically reshaping the landscape.
Was anyone killed during the 1918 Katla eruption?
No fatalities were directly attributed to the eruption. However, the flooding, ashfall and destruction of farmland and infrastructure created severe hardship for nearby communities.
What is a jökulhlaup?
A jökulhlaup is a sudden glacial outburst flood. At Katla, an eruption beneath Mýrdalsjökull can rapidly melt large quantities of ice, releasing water, sediment and icebergs across the surrounding plains.
Why can Katla produce such powerful floods?
Katla is hidden beneath a thick glacier. Heat from an eruption can melt the overlying ice very quickly, allowing a huge volume of water to collect and then escape in a fast-moving flood.
Is Katla an explosive volcano?
Katla’s historical eruptions have predominantly been explosive. When magma interacts with glacial meltwater, it can fragment violently and produce large quantities of ash and tephra. However, the Katla system has also produced major effusive fissure eruptions.
What was the Eldgjá eruption?
Eldgjá was a vast fissure eruption within the Katla volcanic system that began around AD 939. Its fissures extended for almost 80 kilometres, and it produced one of the largest lava flows of the last thousand years.
Could Katla affect air travel?
Yes. A large explosive eruption could send ash high into the atmosphere and disrupt flight routes, as happened during the 2010 eruption of neighbouring Eyjafjallajökull.
Could a Katla eruption affect Vík?
A major eruption could potentially threaten Vík and surrounding infrastructure through flooding, ashfall and disruption to Route 1. Icelandic authorities monitor Katla closely and maintain emergency plans for communities in the area.
What warning signs could appear before a Katla eruption?
Possible warning signs include ground inflation, earthquake swarms, harmonic tremors, increased ice melting, steam and volcanic gas emissions. However, Katla has not produced a major eruption during the era of modern monitoring, so its precise warning pattern remains uncertain.
Can scientists predict Katla’s next eruption?
Scientists cannot determine exactly when Katla will erupt. Monitoring can reveal changing conditions and increasing unrest, but it cannot provide a precise eruption date far in advance.
Does Katla always erupt after Eyjafjallajökull?
No. Although Katla has erupted after some historical Eyjafjallajökull eruptions, the limited evidence does not establish a dependable connection. Most known Katla eruptions have occurred without an eruption at Eyjafjallajökull.
Is Katla overdue for an eruption?
Volcanoes do not follow fixed schedules, so Katla cannot scientifically be described as “overdue.” Historical averages can provide context, but they cannot tell us whether the next eruption will occur soon or many years from now.
Is it safe to visit the Katla area?
The area around Katla and Mýrdalsjökull is a popular destination, but conditions can change. Visitors should always check official updates from the Icelandic Meteorological Office and SafeTravel Iceland and follow any closures or instructions from local authorities.
What is Katla’s connection to Lava Show?
The lava remelted at Lava Show comes from Katla’s 1918 eruption. In Vík, the experience also tells the remarkable story of Lava Show co-founder Júlíus’s ancestor, who narrowly escaped the eruption’s glacial flood while herding sheep on Mýrdalssandur.
Can I see real molten lava near Katla?
At Lava Show in Vík—just a short drive from the Katla area—you can watch real molten lava flow safely indoors. Lava Show also has a location in Reykjavík, giving visitors another opportunity to feel the heat and discover the volcanic forces that have shaped Iceland.
Experience Real Molten Lava
Katla is one of Iceland's most powerful and closely monitored volcanoes, hidden beneath the Mýrdalsjökull glacier and capable of producing spectacular eruptions. While scientists keep a close watch on this sleeping giant, Lava Show offers a unique opportunity to safely experience real molten lava up close. Watch glowing lava flow just metres away and discover the incredible volcanic forces that have shaped Iceland for thousands of years.
Plan your visit:
Experience Lava Show Reykjavík – Watch real molten lava flow in Iceland's capital.
Experience Lava Show Vík – Experience the world's only live lava show just a short drive from Katla on Iceland's South Coast.
Resources cited:
Jökull - The 2011 unrest at Katla volcano: seismicity and geological context
Wikipedia - Largest eruptions of the 21st Century and 20th Century since 1500
Written by Jessica Poteet. Here is an interview with her in the Lava Academy podcast.
