Iceland’s active geology often leads people to question its connection to the Pacific’s famous seismic zone, the Ring of Fire. This intense geothermal activity makes it seem like a natural fit for the world’s major belts of tectonic unrest. However, Iceland’s unique geological setting places it outside the Pacific basin, requiring a different explanation for its fiery nature.
What Defines the Ring of Fire
The Ring of Fire is a roughly 40,000-kilometer belt of intense tectonic activity that encircles the Pacific Ocean basin. This horseshoe-shaped zone contains approximately two-thirds of the world’s active or dormant volcanoes, along with 90% of the world’s earthquakes. Its location is defined by the boundaries of several tectonic plates surrounding the Pacific Plate.
The primary geological process driving the Ring of Fire is subduction, which occurs at convergent plate boundaries. Subduction involves one tectonic plate sinking beneath another, usually an oceanic plate diving under a continental or another oceanic plate. As the subducting plate descends into the Earth’s mantle, it releases water and other volatile compounds that lower the melting point of the surrounding rock. This molten rock, or magma, then rises to the surface, creating the volcanic arcs and mountain ranges that characterize the Ring of Fire, such as the Andes and the Aleutian Islands.
Iceland’s Location and the Tectonic Plate Boundary
Iceland is not a part of the Pacific Ring of Fire, as it is geographically located in the North Atlantic Ocean. It sits directly astride the Mid-Atlantic Ridge (MAR), an immense underwater mountain range that stretches for over 16,000 kilometers.
The MAR represents a divergent plate boundary, where the North American and Eurasian tectonic plates are slowly pulling apart. New crust is continuously created as magma rises from the mantle to fill the gap, solidifying to form new ocean floor. Iceland is the only place on Earth where this major mid-ocean ridge rises above sea level, allowing the rift valley to be observed on land, such as in Þingvellir National Park.
Why Iceland is So Volcanically Active
The intense volcanism in Iceland is a result of a rare geological coincidence: the Mid-Atlantic Ridge intersecting with a massive mantle plume. While the plate separation at the divergent boundary alone causes some volcanic activity, it does not typically create landmasses as large and active as Iceland. Most of the Mid-Atlantic Ridge remains submerged beneath the ocean surface.
A mantle plume is an upwelling of anomalously hot rock that rises from deep within the Earth’s mantle. This Iceland Plume, or hotspot, provides a vast and constant supply of excess magma that interacts with the thinning crust of the divergent plate boundary. The heat from the plume causes a greater volume of rock to melt than would occur at a typical mid-ocean ridge.
This combined activity creates the island’s high concentration of active volcanoes and volcanic systems. The excess magma has built up the ocean floor into a substantial landmass, forming the island of Iceland over the last 20 million years. The ongoing separation of the North American and Eurasian plates, moving apart at a rate of approximately 2.5 centimeters per year, continues to fuel volcanic activity across the rift valley that bisects the country.