Hekla: The Gateway to Hell - Medieval Mythology, the 1104 Cataclysm & Volcanic Fluorosis
Discover Hekla, Iceland's most infamous volcano. Explore its medieval reputation as the entrance to the underworld, the devastating 1104 eruption, and the unique challenges of volcanic ash on Icelandic livestock.
Hekla is arguably Iceland’s most famous and feared volcano. Rising to 1,491 meters in the south of the country, it is not merely a mountain but a 40-kilometer-long volcanic ridge. For centuries, Hekla was known across Europe as the “Gateway to Hell,” a place where the barrier between the mortal world and the eternal fire of the underworld was at its thinnest. Its eruptions are notoriously unpredictable, varying from small explosive events to massive, landscape-altering cataclysms. Beyond the mythology, Hekla serves as a critical natural laboratory for understanding the impact of volcanic ash on agriculture and the long-term history of human settlement in the North Atlantic.
1. The Gateway to Hell: Medieval Mythology and Superstition
In the Middle Ages, Hekla was more than just a volcano; it was a psychological landmark for Christendom. The stories that filtered back to mainland Europe painted a terrifying picture of the Icelandic peak.
The Cistercian Connection
Much of Hekla’s “demonic” reputation stems from the writings of Cistercian monks in the 12th and 13th centuries. Following the massive eruption of 1104, the monk Herbert of Clairvaux wrote in his Liber Miraculorum that the volcano was the literal entrance to the inferno. He claimed that the screams of the damned could be heard echoing from its craters during eruptions. This was not merely local folklore; it was a widely accepted “fact” in medieval Europe, used by the Church to illustrate the reality of hell to a far-off population.
Witches and the Devil
Icelandic folklore also added its own layers of dread. It was believed that Hekla was the gathering place for witches and the devil on Easter night. Local stories told of “Hidden People” (Huldufólk) fleeing the mountain’s wrath, and of ravens—thought to be spirits of the damned—circling the peak in search of souls to carry into the abyss. This aura of terror was so potent that Hekla remained unclimbed for centuries; it wasn’t until 1750 that naturalists Eggert Ólafsson and Bjarni Pálsson reached the summit, finally proving that there were no demons or gateways to be found, only scorched rock and ice.
2. The 1104 Cataclysm: Hekla’s First Historical Eruption
Before 1104, the Vikings who settled Iceland were largely unaware of Hekla’s power. That changed in an instant with the volcano’s first recorded eruption in historical times—a VEI 5 event that remains one of the largest in Iceland’s history.
The Destruction of Þjórsárdalur
The 1104 eruption was explosive and sudden, occurring without the seismic warnings we rely on today. It ejected an estimated 2 cubic kilometers of tephra (volcanic ash and rock) into the atmosphere. The ash fall was so heavy that it buried entire communities. The most famous casualty was the valley of Þjórsárdalur, a thriving agricultural settlement at the time.
Archaeologists have excavated over 20 farms in the valley that were abandoned and preserved under layers of white pumice. The most notable is Stöng, a large Viking-age longhouse that was impeccably preserved, much like the ruins of Pompeii. Today, a reconstruction of Stöng allows visitors to see exactly how these medieval farmers lived before Hekla erased their world in a single afternoon.
Impact on European Climate and Archaeology
The 1104 eruption was so powerful that its ash plume reached mainland Europe, causing a “volcanic winter” that led to crop failures and famine in several regions. In modern times, this ash has become a vital tool for scientists. The 1104 tephra layer acts as a “chronological marker” or isochrone across the North Atlantic. Because the date of the eruption is known precisely from historical records, archaeologists who find this specific layer of white pumice in a dig can instantly date the artifacts surrounding it.
This science, known as tephrochronology, was largely pioneered in Iceland during the 20th century. Hekla’s distinct footprints—layers of black, brown, and white ash—provide a timeline for the last several thousand years of human and environmental history in the region, allowing researchers to track the rise and fall of Viking-age settlements with incredible precision.
3. The 1947 Eruption: A Modern Giant Awakes
After nearly a century of relative silence, Hekla erupted on March 29, 1947, in an event that would last for over a year. This was one of the most thoroughly studied eruptions of the pre-satellite era. It began with an explosion that sent an ash column up to 30 kilometers into the atmosphere—the highest ever recorded at the time.
The 1947 event produced a massive volume of lava, covering over 40 square kilometers of land. It was during this eruption that scientists first realized the sheer variety of Hekla’s “lava character.” The mountain produced both viscous, slow-moving blocky lava and more fluid pahoehoe-like flows. This eruption also highlighted the danger of volcanic gases; while the ash was a threat to livestock, the release of sulfur dioxide caused significant local respiratory issues and acid rain that damaged vegetation miles from the crater.
4. The Silent Killer: Volcanic Fluorosis and Livestock
While the fire and lava are the most visible threats, Hekla poses a more subtle and deadly danger to the Icelandic way of life: fluoride poisoning.
The Ash of Fluorosis
Hekla’s ash is uniquely high in fluorine. When the volcano erupts, fine-grained ash settles on the vast pastures where Iceland’s sheep and horses graze. Even a thin layer of ash—invisible to the naked eye—can contain lethal concentrations of soluble fluoride. As livestock eat the contaminated grass, the fluoride enters their system, leading to a condition known as fluorosis.
Clinical Impact
Fluorosis is a agonizing way for an animal to die. It attacks the skeletal structure and teeth. In growing animals, it prevents the formation of tooth enamel, causing teeth to crumble and preventing the animal from eating. In older animals, it causes bones to become brittle or grow abnormal spurs, leading to lameness and eventual death.
The 1970 eruption of Hekla was particularly devastating in this regard, killing approximately 8,000 sheep and hundreds of horses across southern Iceland. This recurring threat forced Icelandic farmers to develop sophisticated emergency protocols, including moving livestock indoors and providing clean feed the moment Hekla shows signs of waking.
4. Unpredictability: The “Hekla Style” of Erupting
Volcanologists use the term “Hekla-style” to describe the volcano’s unique and dangerous behavior. Unlike many volcanoes that follow a predictable pattern, Hekla is a master of disguise.
No Warning
Most volcanoes provide weeks or even months of “pre-cursor” activity, such as increased earthquakes or ground swelling. Hekla, however, often provides as little as 30 to 80 minutes of warning before magma breaches the surface. This makes it one of the most dangerous mountains in the world for hikers. In the 2000 eruption, scientists only had enough time to issue a radio warning an hour before the mountain exploded.
The Relationship with Time
There is a direct correlation between the length of Hekla’s dormancy and the explosiveness of its next eruption. The longer Hekla stays quiet, the more silica-rich (and therefore more explosive) the initial magma becomes. Because Hekla has been quiet since 2000—longer than its typical 10-year cycle—scientists are increasingly concerned that the next eruption will be significantly larger and more violent than the last several events.
5. Hekla in Modern Iceland: Tourism and Monitoring
Today, Hekla is a major draw for tourism, but it remains a mountain that demands respect.
Hiking the “Hooded One”
The name “Hekla” literally means “short hooded cloak,” referring to the frequent clouds that shroud its summit. On a clear day, the hike to the top provides a stunning view of the Icelandic highlands. However, hikers are now encouraged to carry GPS devices that can receive emergency alerts, as the window for evacuation is incredibly small.
High-Tech Surveillance
Because of the short warning time, Hekla is now one of the most heavily instrumented volcanoes on Earth. A network of strainmeters, buried 200 meters into the crust, detects the minute “stretching” of the rock that occurs when magma begins its final dash to the surface. Infrared satellites also scan the peak for thermal anomalies that might indicate an imminent breach.
6. Frequently Asked Questions (FAQ)
Is Hekla overdue for an eruption?
Statistically, yes. For much of the 20th century, Hekla erupted roughly every 10 years (1947, 1970, 1980, 1991, 2000). Having been quiet for over 24 years, it is currently in a state of high tension.
Can Hekla affect flights like Eyjafjallajökull did?
Potentially, yes. While Hekla is not subglacial (so it doesn’t have the same “fire-meets-ice” ash generation), its eruptions can reach altitudes of 15 kilometers or more. This could easily disrupt international flight paths over the North Atlantic.
What should I do if I am on Hekla during an eruption?
Run. If you feel earthquakes or see steam rising from the ground, you have to move away from the summit immediately. The primary danger on Hekla is not just lava, but the supersonic blast of ash and gas that can occur within minutes of the first tremor.
Are there any towns on Hekla?
There are no towns on the volcano itself, but there are several large farming communities and tourist centers (like Hella and Flúðir) within the danger zone. These communities have well-rehearsed evacuation plans.
Technical Specifications
| Feature | Data |
|---|---|
| Elevation | 1,491 m (4,892 ft) |
| Type | Stratovolcano / Volcanic Fissure |
| Frequency | Historically unpredictable, 20th-century avg: ~10 yrs |
| Main Hazard | Explosive ash plumes, Fluoride poisoning, Short warning time |
| Longest dormancy | Historically up to 120 years, currently 24+ years |
| Historical Status | ”Gateway to Hell” (Middle Ages) |
Hekla is a reminder of the raw power that pulses beneath the Icelandic soil. Whether viewed as a gate to the underworld or a complex geological engine, it remains a mountain that the world cannot afford to ignore.