Iceland’s Ongoing Eruption Could Last Years or Decades

Aerial view of lava flowing from the Geldingadalur crater and the audience gathered to admire it

It’s been three months since the eruption in Geldingadalir, Iceland began and experts say it could be years or even decades until it is over. If it does indeed last for decades, lava could reach the nearby town of Grindavík as well as Svartsengi power station. The eruption’s slow and steady flow could eventually form what’s known as a shield volcano: a broad and gently-sloping mountain of which Iceland has some fine examples.

“If we look at what would be the most extreme picture, that if this eruption lasts for 50 years, then we are creating another Skjaldbreiður mountain,” Volcanologist Þorvaldur Þorðarson told RÚV. Skjaldbreiður is a 1,060 metre high shield volcano located in West Iceland that was formed by a long eruption some 9,000 years ago. “If we place Skjaldbreiður directly on top of [the current eruption at] Fagradalsfjall, then it is easy to draw a radius around it and see what a large area the lava could cover and it’s a fairly large area.”

Read More: Road Sacrificed, Town Protected

Though it may not be affected by the eruption for decades (if ever), protective structures are already being designed for the nearby town of Grindavík in case lava from the eruption begins flowing toward it. Authorities experimented at the eruption site by creating earthen barriers to direct the lava. Though lava eventually collected high enough to flow over the barriers, it did not breach them, proving the effectiveness of the design.

Golli. The protective barriers were made from material found on-site and were meant to slow down the lava flow by allowing the lava to pool and gather.

Eruption Marks Beginning of Active Period

Iceland is located on a rift between the North American and Eurasian tectonic plates, and the rift cuts across the Reykjanes peninsula from west to east. As the plates move apart they create tension in the earth’s crust that is released in the form of earthquakes or – more rarely – eruptions. Geologic activity on the peninsula is characterised by volcanic periods lasting 400-500 years alternating with seismic periods lasting 600-800 years. The ongoing eruption is the first in the region in nearly 800 years, indicating that it marks the end of a seismic period and the beginning of a period of volcanic activity.

In Focus: The Geology of the Reykjanes Peninsula

Another factor makes the Geldingadalir eruption special. While in most eruptions the source of the magma is a chamber relatively close to the earth’s surface, the magma feeding the Geldingadalir eruption is coming straight from the earth’s mantle. It’s been around 7,000 years since such an eruption has occurred on the Reykjanes peninsula.

Reykjanes Eruption: Road Sacrificed, Town Protected

Geldingadalir reykjanes eruption volcano

Icelandic authorities will not attempt to divert lava from the ongoing eruption in Geldingadalir away from the adjacent Suðurstrandarvegur road. The eruption has been ongoing for more than three months now and its growing lava field is expected to reach the road in one to three weeks. Efforts will instead be focused on protecting the nearby town of Grindavík and Svartsengi power station if necessary.

“We’ve had many meetings over the past days and weeks and assess whether it’s feasible to protect Suðurstrandarvegur,” Fannar Jónasson, Mayor of Grindavík, told RÚV. “After a thorough review it was decided that it wouldn’t work, both for technical reasons, due to time, and not least due to the cost.” Fannar says authorities are now looking further ahead to see what infrastructure will need protecting if the eruption continues for many more months. “If it continues for a few months or years we might have to respond so it doesn’t flow to Svartsengi [power station] or even Grindavík. We want to have enough time to prevent that and create powerful barriers. That wouldn’t happen for a long time but structures are being designed nevertheless that would provide protection in that case.”

While geologists say there is no way to predict how long the Reykjanes eruption will last, several have stated that it could be a shield volcano in the making. Shield volcanoes are formed by long, slow eruptions like the one in Geldingadalir where lava forms a gently sloping volcano over time. Such eruptions have rarely occurred in Iceland since the end of the Ice Age but they can last years at a time.

Long Eruption on Reykjanes Could Form Shield Volcano

People admiring the Reykjanes peninsula eruption from the edge of the flowing lava

There is no way to tell how long the ongoing eruption on Iceland’s Reykjanes peninsula will last, experts say. Yet if it continues, the slow-flowing, highly fluid lava could potentially form a shield volcano, like Hawaii’s Mauna Loa, often cited as the largest volcano on earth.

The Geldingadalur eruption has now been ongoing for nine days with a steady rate of flow between 5-7 cubic metres per second, according to the Icelandic Met Office. The lava flow is filling Geldingadalur valley, where the erupting fissure is located. “If the eruption keeps at a similar rate, it is modelled that the lava will flow east towards Merardalur valley,” a tweet from the Met Office states. “If the volcano continues to erupt it could end up being categorised as a shield volcano.”

Shield volcanoes are gently-sloping, often large volcanoes, usually formed over long periods of time. The lava fields from such volcanoes can extend several kilometres around their source. The lava emitted by the Geldingadalur eruption is highly fluid – this means it travels further and forms thinner layers than more viscous lava. Over time, such layers can form the gently-rounded shape of a shield volcano, thus named due to its resemblance to a warrior’s shield lying on the ground. These types of volcanoes are more commonly formed at continental rifts such as the one cutting across the Reykjanes peninsula. Iceland does have other shield volcanoes, including Skjaldbreiður (1,060m, whose name is roughly translated as “broad shield”) and Trölladyngja (1,468m), the country’s biggest volcano of that sort. Most of Iceland’s shield volcanoes were formed thousands of years ago.

While experts cannot say how long the Geldingadalur eruption will last or whether it will in fact form a shield volcano, the lava’s deep source and slow but steady flow indicate a long eruption could be ahead.