Eldfell is classified as a scoria cone volcano, a relatively small and steep-sided volcanic structure. It formed dramatically during a five-month eruption that began without warning on January 23, 1973, on Heimaey, Iceland. Heimaey is the largest and only inhabited island in the Vestmann Islands archipelago, located off Iceland’s southern coast. The sudden appearance of this new mountain, whose name translates to “Hill of Fire,” created a crisis for the local community and permanently reshaped the island’s geography.
Defining the Scoria Cone Volcano
A scoria cone, often called a cinder cone, is the smallest and most numerous type of volcano globally. This form is built almost entirely from the explosive ejection of molten fragments, known as pyroclastic material or scoria, which cool rapidly in the air before falling back around the vent. This process, typically resulting from Strombolian-style eruptions, creates a symmetrical, conical hill with steep slopes, often reaching inclinations of up to 35 degrees.
The cone consists of highly vesicular, glassy basaltic fragments, often the size of lapilli or cinders. Scoria cones typically feature a distinct bowl-shaped crater at their summit, formed by the final explosive phases of the eruption. Unlike massive shield or stratovolcanoes, scoria cones are usually monogenetic, meaning they result from a single, relatively short eruptive episode lasting from a few days to a few years. Eldfell, which stands at approximately 200 meters tall, fits this profile, a product of a singular, intense burst of activity. The loosely piled fragments are easily eroded, contributing to the relatively short geological lifespan of this volcano type.
Geological Setting and Formation
Eldfell’s formation is tied to Iceland’s active tectonic environment, situated directly astride the Mid-Atlantic Ridge. The Vestmann Islands (Vestmannaeyjar) are part of the South Iceland Seismic Zone and the Eastern Volcanic Zone, marking an area where the North American and Eurasian tectonic plates are pulling apart. This rifting motion allows magma to rise close to the surface, fueling the volcanic activity.
The 1973 eruption began with a fissure opening on the eastern side of Heimaey, cutting through the residential area and extending approximately 1.6 kilometers. Initially, lava fountained along the entire length of the fissure, but within hours, the activity localized to a single vent. This concentration of eruptive force resulted in the rapid accumulation of tephra and scoria around that point, which built the Eldfell cone. The new volcano formed adjacent to the older cone of Helgafell, which had erupted about 5,000 years prior, demonstrating the continuous, localized nature of volcanism in this rift zone.
The 1973 Eruption and Human Intervention
The eruption began just after midnight on January 23, 1973, immediately impacting the fishing town of Vestmannaeyjar. The location was hazardous, occurring just a few hundred meters from the town’s eastern edge. The initial activity forced the swift evacuation of nearly all of Heimaey’s 5,300 residents, primarily utilizing the fishing fleet docked in the harbor.
The primary threat quickly became the flow of thick, blocky ‘a’ā lava and the fallout of volcanic ash (tephra). Ashfall buried hundreds of homes, while the lava flow advanced toward the harbor, the island’s economic lifeline. Had the harbor entrance been sealed by the lava, the island’s future would have been severely compromised.
In a pioneering effort, authorities launched an operation to stop the advancing lava by cooling it with seawater. Starting in early February, a system was devised to pump massive volumes of cold seawater directly onto the front and sides of the lava flow. The goal was to rapidly solidify the outer crust, creating a barrier that would divert the flow or cause the interior to congeal.
This unprecedented effort required the deployment of thirty-two high-capacity pumps, many flown in from the United States, to deliver millions of cubic meters of water. The continuous application of cold seawater onto the 1,100°C lava created a thick, solid rock barrier, succeeding in slowing and stopping the flow just short of closing the harbor. The five-month eruption and subsequent cooling operation saved the harbor, while also adding over two square kilometers of new land to Heimaey.