Iceland is a volcanic island, a landmass built by the continuous outpouring of magma from beneath the Earth’s surface. Its existence above the North Atlantic is a direct result of intense, persistent volcanic activity. The island’s landscape is a dynamic tapestry woven from basalt, ash, and ice, confirming its identity as a geological creation shaped by fire. This constant renewal of the crust makes Iceland one of the most volcanically active regions on the planet.
The Geological Setting
Iceland’s unique geology is a consequence of a dual mechanism occurring deep within the Earth. The island is situated directly across the Mid-Atlantic Ridge (MAR), which marks the boundary between the North American and Eurasian tectonic plates. These two plates are pulling apart, a process known as seafloor spreading. This divergence creates a rift zone where magma from the underlying mantle rises to fill the gap, constantly forming new oceanic crust.
The plates are separating at an average rate of about 2.5 centimeters per year. What makes Iceland exceptional is that the Mid-Atlantic Ridge, which is submerged for almost its entire length, rises above sea level here. This phenomenon is explained by the presence of a deep-seated mantle plume, or hotspot, located directly beneath the island. This plume is an upwelling of rock that is significantly hotter than the surrounding mantle.
The plume provides an immense volume of excess magma and heat to build a massive landmass that rises thousands of meters from the ocean floor. Geophysical studies suggest this mantle plume has an excess temperature of 150 to 200 Kelvin compared to the typical mantle material. This high-temperature anomaly causes a greater degree of melting, resulting in the anomalously thick crust beneath Iceland, which can be up to 40 kilometers thick in some areas. The combination of the divergent plate boundary and the plume creates a sustained and prolific magmatic system.
Active Volcanic Systems
The intense heat and magma generation manifest in approximately 30 active volcanic systems across the island, categorized into two main types. One common manifestation is the Fissure Volcano, characterized by linear eruptions along cracks parallel to the rift zones. These eruptions are often effusive, producing vast quantities of basaltic lava that spreads out to form extensive fields and plateaus. Historical examples, such as the Laki eruption in 1783, demonstrate the scale of lava output from these elongated vents.
The other major type is the Central Volcano, a large, composite structure often featuring a central magma chamber and a summit caldera. Examples like Hekla and Katla are typically cone-shaped stratovolcanoes. These central volcanoes are often capped by glaciers, which leads to a specific hazard. When a subglacial eruption occurs, the magma rapidly melts the overlying ice cap, generating massive volumes of meltwater.
This meltwater mixes with volcanic ash and debris, resulting in sudden, violent glacial outburst floods known as jökulhlaups. Eruptions involving the interaction of magma and water—called hydromagmatic events—are particularly explosive. They produce fine ash clouds that can travel long distances, as demonstrated by the 2010 eruption of Eyjafjallajökull.
Geothermal Consequences
The shallow magma and high heat flow create one of the world’s most extensive geothermal energy resources. This deep-seated heat is harnessed to provide energy for the nation’s infrastructure. In a process known as district heating, approximately 90% of all homes in Iceland are heated directly by geothermal water and steam piped from the ground. This system utilizes a vast network to deliver clean, low-cost heating to the population.
In addition to heating, the geothermal resource is used for electricity generation, accounting for about 25 to 30% of the country’s total power production. Five major power plants tap into high-temperature reservoirs, converting the steam and hot water into electrical energy. The heat is also utilized for warming greenhouses to grow local produce and maintaining outdoor swimming pools and spas, including the famous Blue Lagoon.
The non-eruptive surface features of this subterranean heat are evident across the landscape in the form of hot springs, steam vents (fumaroles), and geysers. Geysers, such as the famous Strokkur, are reminders of the superheated water circulating deep below the crust. They intermittently erupt plumes of steam and water into the air. This constant, accessible thermal energy is a defining characteristic of Iceland.