Katla, a powerful volcano, is hidden beneath the Mýrdalsjökull ice cap in southern Iceland. This geological feature is known for its potential to trigger significant events, making it a subject of continuous scientific interest. Katla represents a considerable force within Iceland’s dynamic volcanic landscape, drawing attention due to its past and potential future impact.
Katla’s Volcanic Identity
Katla is classified as a subglacial caldera volcano, a unique combination that defines its eruptive style and associated hazards. A caldera is a large, basin-shaped depression that forms when a volcano’s magma chamber empties during a major eruption, causing the ground above it to collapse inward. Katla’s caldera spans approximately 10 to 14 kilometers in diameter and is covered by an ice layer ranging from 200 to 700 meters thick.
The term “subglacial” means the volcano is situated beneath a glacier, specifically the Mýrdalsjökull ice cap. This icy overlay significantly influences how Katla erupts and the phenomena it produces. Katla’s location on the Mid-Atlantic Ridge, where the North American and Eurasian tectonic plates are pulling apart, further contributes to its high level of volcanic activity.
The Impact of Ice and Magma
The interaction between Katla’s magma and its overlying glacial ice creates distinct eruptive phenomena. One significant consequence is the generation of jökulhlaups, sudden, massive glacial outburst floods. These floods occur when heat from rising magma rapidly melts large volumes of glacial ice, causing water to accumulate beneath the glacier until it bursts forth with immense force.
Jökulhlaups can be highly destructive, as evidenced by the 1918 eruption, where floodwaters reached peak flows of hundreds of thousands of cubic meters per second and extended Iceland’s southern coastline by several kilometers due to sediment deposition. Additionally, eruptions beneath ice can produce particularly fine and widespread ash plumes. The rapid cooling and fragmentation of magma when it encounters water leads to the creation of highly pulverized ash, which can travel great distances and pose aviation and environmental challenges.
A History of Activity and Vigilance
Katla has a well-documented history of activity, with at least 20 to 21 major eruptions recorded since the 10th century. Historically, it has erupted roughly every 40 to 80 years. The last major eruption occurred in 1918, marking a period of dormancy that has now extended for over a century, among the longest in its known history. While minor events and increased seismic activity have been observed in recent decades, including in 1955, 1979, 1999, and 2011, none have resulted in a major breakthrough eruption.
Katla is under continuous and close monitoring by Icelandic scientists due to its potential for significant impact. Monitoring efforts include tracking seismic activity, such as earthquakes and tremors, and observing ground deformation, which can indicate magma movement beneath the surface. Changes in glacial meltwater, including its electrical conductivity and the formation of ice cauldrons, also provide important clues about the volcano’s geothermal state. These comprehensive monitoring systems provide early warnings to local communities and authorities.