Iceland is defined by its dramatic landscape of glaciers, geysers, and fire. Its frequent volcanic activity has shaped its geography and captured global attention. To determine how many volcanoes are active, one must understand how scientists classify these features, clarifying the difference between individual mountains and interconnected volcanic systems.
Understanding Volcanic Activity in Iceland
The geological classification of an active volcano is nuanced. In Iceland, a volcano or system is generally deemed active if it has erupted within the Holocene Epoch (the last 10,000 to 12,000 years). This extensive timeframe accounts for the long repose periods common to many large volcanoes, which can remain quiet for centuries before becoming active again.
Icelandic volcanism is organized around larger structures called volcanic systems, rather than isolated peaks. A system typically consists of a central volcano, often featuring a caldera, and an associated fissure swarm. Eruptions can occur at the central volcano or along the fissure swarm, making the system the fundamental unit of volcanic activity. This explains why Iceland has over a hundred volcanic mountains but a much smaller number of active systems.
The Official Count of Active Volcanic Systems
The Icelandic Meteorological Office and the Institute of Earth Sciences recognize 32 active volcanic systems within the country’s main volcanic zones. These systems have erupted since the last Ice Age and maintain the potential for future activity. They are concentrated along a southwest to northeast axis following the tectonic plate boundary.
Some systems are known for frequent and powerful eruptions, such as Grímsvötn, the most active system, which lies beneath the Vatnajökull ice cap. Other prominent systems include Katla, a subglacial volcano beneath Mýrdalsjökull, and Hekla, known for unpredictable events. Recently, the Reykjanes Peninsula, including the Fagradalsfjall and Svartsengi systems, reawoke after centuries of dormancy. These systems are the primary sources of magmatic activity and seismic unrest.
Iceland’s Unique Geological Setting
Iceland’s intense volcanism results from a rare combination of two powerful geological forces. The island straddles the Mid-Atlantic Ridge, a divergent plate boundary where the North American and Eurasian tectonic plates are moving apart. These plates are separating at about two centimeters per year, creating fractures in the crust through which magma can ascend.
Directly beneath this spreading boundary lies a deep-seated mantle plume, often called the Iceland Hotspot. This plume is an upwelling of hot material from deep within the Earth’s mantle, generating immense magma volume. The combination of tectonic rifting and the mantle plume explains why the Mid-Atlantic Ridge, which is mostly submerged, rises above sea level, creating the island itself. This continuous heat provides the fuel for the 32 active volcanic systems.
How Scientists Monitor Volcanic Risk
The classification of an active system is supported by comprehensive monitoring by the Icelandic Meteorological Office (IMO) and the University of Iceland. Scientists employ an extensive network of instruments to detect signs of magma movement beneath the surface. One primary method is seismic monitoring, which records the thousands of small earthquakes generated as magma pushes through underground rock layers.
Ground deformation is tracked using Global Positioning System (GPS) stations and satellite-based radar technology called Interferometric Synthetic Aperture Radar (InSAR). These techniques detect changes in ground elevation, or “volcano inflation,” down to a few millimeters, indicating a swelling magma chamber. Scientists also monitor the release of volcanic gases, as changes in composition or volume can signal that magma is nearing the surface. This data allows authorities to assess when an active system shifts from general unrest to an imminent risk of eruption.