Iceland is so Volcanically Active: Here's Why

Tuesday - November 28 2023, 22:19 UTC - 11 months ago

Iceland is a geologically active place. It's overactivity is a result of two features. One is called a hotspot, and the other involves two tectonic plates that are pulling apart right beneath the island. Radar satellite data shows that a broad area around Grindavík sank by 3 feet over 10 days and a GPS station in town moved 3 feet to the southeast from Oct. 28 to Nov. 9. Magma pressurised beneath the earth has led to potential of an eruption.

Thousands of earthquakes in recent weeks have shaken the Icelandic fishing town of Grindavík, about 30 miles (50 kilometers) southwest of the capital Reykjavik. They have triggered evacuations and warnings that a volcanic eruption may be imminent.While the idea of magma rising was no doubt scary for tourists visiting the nearby Blue Lagoon geothermal spa, which was closed as a precaution, Iceland’s residents have learned over centuries to live with their island’s overactive geology .

So, why is Iceland so volcanically active?The answer has two parts: One has to do with what geologists unimaginatively call a hotspot, and the other involves giant tectonic plates that are pulling apart right beneath the island. As a geologist, I study both.Life on the edge of two tectonic platesWhen plate tectonic theory was emerging in the 1960s, geologists realized that many volcanoes are located in zones where tectonic plates meet .

Tectonic plates are gigantic chunks of Earth’s rigid outer layer that carry both continents and oceans and are constantly in motion. They cover the planet like large pieces of a spherical jigsaw puzzle.Many of these volcanoes are in subduction zones, like the Pacific’s Ring of Fire, where thinner oceanic plates slowly sink into Earth’s mantle. These are the postcard stratovolcanoes like Mount Fuji, in Japan, or Mount Rainier, outside of Seattle .

Because of their high gas content, they tend to erupt catastrophically, shooting ash high into the atmosphere with the energy of nuclear bombs, as Mount St. Helens did in 1980.A second, typically quieter kind of volcano forms where plates pull apart.The volcanic activity near Grindavík is directly related to this kind of plate tectonic motion. The mid-Atlantic ridge between the Eurasian and North American plates cuts right through that part of the island .

In fact, at Thingvellir National Park you can literally walk between the two tectonic plates. You can see the topographic scars of the rift in the long, linear valleys that extend to the northeast from Grindavík. They align with the recent swarm of earthquakes and the ground deformation that is happening.Radar satellite data from the Icelandic Meteorological Office show that a broad area around Grindavík sank by about 3 feet (1 meter) over 10 days, and the GPS station in town moved about 3 feet (1 meter) to the southeast with respect to the North American plate from Oct .

28 to Nov. 9. Large cracks have broken streets and houses in Grindavík.Where plates pull away from each other, the underlying mantle rises toward the surface to fill the gap, carrying its heat with it and moving into an area of lower pressure. Those two processes cause melting at depth and volcanic activity at the surface.Starting in October 2023, this pressurized magma began pushing its way along a fissure toward the surface, triggering the earthquake swarms and creating the possibility of an eruption .

This is the same process that creates new oceanic crust underwater at mid-ocean ridges. After the magma solidifies as basalt rock, it will look like vertical walls intruded into the surrounding area. The Grindavík dike appers to be 50-100 m long and could be as deep as 2-3 km depending on where the magma is moving.