Iceland’s Volcanoes

Skútustaðir pseudocraters, Lake Mývatn
Iceland's volcanic activity created craters along Lake Mývatn.
Hexagonal columns at Reynisfjara, South Coast
Formed by lava cooling slowly over time, the hexagonal rock columns at Reynisfjara are an awe-inspiring example of columnar jointing.
By Rick Steves and Ian Watson

Many travelers come to Iceland hoping for a glimpse of a volcano, especially after the one called Eyjafjallajökull grabbed the world's attention in 2010 by spewing ash into the atmosphere — and bringing European air travel to a halt.

Iceland is among the most volcanically active places in the world, with roughly one eruption every five years. Aside from liquid lava, Iceland's volcanoes eject gas, ash, cinders, and solid rock (like pumice). The biggest rocks are sometimes called "volcanic bombs." Volcanic eruptions can last from a couple of days to several years.

Grímsvötn, a hard-to-reach volcano under the Vatnajökull glacier (in Southeast Iceland), is currently Iceland's most active; it last erupted in May 2011. The more famous Eyjafjallajökull, on the South Coast, has been quiet since its erupton in 2010. Other well-known Icelandic volcanoes include nearby Katla, which has the most potential for a damaging eruption (as it could send a tidal wave rushing down over the South Coast), along with Hekla (once nicknamed the "Gateway to Hell"), Krafla, and Askja.

Of the roughly 130 volcanoes in Iceland, the most common type is the stratovolcano — the classic cone-shaped peak with explosive eruptions that form a crater in the very top (such as Hekla and Katla, on the South Coast). There are also a few dormant shield volcanoes — with low-profile, wide-spreading lava flows; one called Skjaldbreiður is near the Golden Circle. Eruptions from fissure vents — long cracks in the earth's crust — are also common in Iceland, such as the Holuhraun eruption of 2014 and the destructive Laki eruptions in the 1780s.

While you probably won't see any spewing ash or flowing lava on your next trip to Iceland, you can easily visit a variety of volcanic sights to learn more about the island's unique geology.

The Westman Islands, an archipelago just off Iceland's South Coast, are themselves the country's most interesting volcano-related sight, where you can see the results of some of Iceland's most spectacular recent volcanic activity. Between 1963 to 1967, the islet of Surtsey — which you can see from the main island of Heimaey — literally rose from the Atlantic Ocean. On Heimaey, in the town of Vestmannaeyjar, you can see streets that dead-end at steep walls of volcanic rock: a result of a surprise eruption one night in 1973, when the eastern part of town was gradually swallowed by flowing lava. And Vestmannaeyjar's Eldheimar Museum is built around a house buried by lava — letting you peek into a family home forever trapped in rock.

Iceland's entire surface is made of volcanic rock, most of it basalt — the rock that forms when lava cools. Iceland's towering cliffs and jagged islands and skerries are all made of basalt. When basalt cools in particular ways, it forms the hexagonal rock columns that you can see at Reynisfjara (on the South Coast) and other places.

New lava is shiny and oily-looking, while old lava loses its gleam. Old lava fields — recognizable by their unique, bumpy appearance — are often covered by a fuzzy layer of Icelandic moss.

At the lake called Mývatn, in northern Iceland, you can see pseudocraters (also called "rootless cones"), which form after lava flows cover a pond or marsh. The water underneath the lava boils and a giant bubble breaks through the lava, leaving a crater-like depression.

So why does Iceland have so many volcanoes? The answer lies beneath the surface. Iceland is located on the long, mostly underwater Mid-Atlantic Ridge — the meeting point of the Eurasian and North American tectonic plates. As the two tectonic plates move apart, magma from the earth's mantle rises to the surface (we start calling it "lava" when it erupts). Iceland is located on a mantle plume, where magma is especially close to the surface, which explains why land formed in this spot in the middle of the ocean, and not elsewhere along the tectonic ridge.

Ian Watson is the co-author of the Rick Steves Iceland guidebook.