There are hundreds of volcanic cones dotting the landscape of Iceland. Most are extinct, of course — although there are eruptions every few years that remind everyone that Iceland isn’t quite docile yet.

The stark and rocky sides of volcanic craters are a huge tourist attraction in Iceland — climbing to the rims of extinct volcanoes for spectacular views over the country, hiking up glaciers that slide inexorably over rumbling volcanoes hundreds of meters below, walking through the vast fields of moss-covered lava, spelunking in mile-long lava tubes, you name it, there is an allure to these remnants of Iceland’s livelier past. Many of the most astounding sights in Iceland are volcanoes — and not just the quiet ones.  Whenever there is a live eruption anywhere in Iceland, throngs of tourists flock to see the lava flows and clouds of ash.

Shield volcanoes

Shield volcanoes are usually low, mound-shaped hills that are gently sloping and built up from layers of fast-flowing lava. For volcanoes, they are fairly gentle, although lava may flow out over the growing hill for miles. This type of volcano is familiar in Hawaii — Kilaueua and Maunaloa are enormous shield volcanoes, erupting often but without much violence and covering the land around them with layer after layer of flowing rock.

Stratovolcanoes

Also called ‘composite’ volcanoes. Stratovolcanoes are the stuff seen in disaster movies — huge eruptions with smoke and ash and lava. These are the explosively erupting volcanoes that flatten cities and blast out clouds of steam, ash, rock and dust. In some cases, there is actually very little lava in the eruption — the pyroclastic flow is what does the damage. Lava eruptions are thick and cannot flow far down the cone before hardening.

They are much steeper than the flatter shield volcano type, although built by the same sort of accretion of layers of lava and ash. Many are thousands of feet high. Mount St Helens is a stratovolcano, as is Vesuvius. This is the most common form of volcano on earth, and tend to cluster in zones where one tectonic plate is pushing beneath another (subduction zones).

Scoria cones

Scoria, or cinder cone volcanoes are usually small and made up of cinders and ash, but very little lava. They are often very steep-sided, but are looser accumulations of rock and cinder ejected high into the air and falling back around the crater and downwind of a vent of lava. Lava eruptions from  a cinder cone usually seep from underneath the crater, often carrying off part of the cone itself, since the soft-sided volcano isn’t strong enough to hold up the rise of lava within the crater. The cinders and rocks making up the volcano are called tephra.

Most scoria craters are the result of a single eruption, and the volcanoes tend to be small. They are also common on the sides of larger volcanoes.

Volcanoes in Iceland

Iceland exists because of a large volcanic hotspot straddling the ridge between the North American plate and Eurasian plate.  There are thirty active volcanic systems; eruptions in the last few years have included the tongue-twisting Eyafyallajókull (2010), Grimsvötn (2011), and Bárðarbunga (2014).  Many of the volcanoes in Iceland are embedded under the island’s many glaciers, which can generate life-threatening flooding when the heat from the volcano melts the underside of the glacier.

Hekla, in south Iceland, has been rumbling a lot lately, and experts are issuing warnings to travelers to avoid the area, as it could erupt with little warning (june 2016).