Centuries ago, Icelanders believed that volcanic flares were human souls, hurled from the inferno. Even today, folk tales speak of elves who skulk among the lava fields, jealously guarding the land.

In Iceland’s northern interior, where stagnant pools belch sulphurous gas and volcanic debris is scattered across plains, these myths are especially dark. Fables passed down orally through generations describe the Krafla volcano as a portal to hell. In fact, it’s where the devil landed after being expelled from heaven.

Today, Krafla broods quietly, its 10km-wide caldera sitting along the Mid-Atlantic ridge, the seam dividing Iceland between the North American and Eurasian tectonic plates. But Krafla was not always so calm. This year marks 40 years since the 1975 start of the Krafla fires, a nine-year period of extraordinary geological activity in which nine huge eruptions occurred, plumes of lava burst from 1,138m-deep fissures and an enormous magma chamber formed.

Despite Krafla’s infernal reputation – or perhaps because of it – the volcano is easy to explore. In northern Iceland, it seems, the road to hell is paved with wooden walking trails.

As I walked along the pathways that spiral around Krafla’s caldera, winding through smouldering blackened lava fields, I could feel the heat of the Earth through my shoes. Steam hissed through clefts bearing the reddish tinge of iron.

The caldera is home to two craters, Leirhnjúkur and Víti, the latter of which translates directly to “hell”. Towards Leirhnjúkur crater, noxious bubbles created ripples in the jade-coloured mud pools. Their sulphurous tang made my eyes water.

Lava fields like these were once thought to be battlefields presided over by the gods. Even today, local folklore links volcanic landscapes to trolls, pugnacious beings who lurked below ground and were turned to stone by sunlight. Many of the scarred boulders around Krafla resemble crouching gnomes.

“All societies have superstitions and beliefs that exist in spite of all that Richard Dawkins can throw at them,” explained Terry Gunnell, a professor of folkloristics at the University of Iceland. “Iceland is on the periphery, and nature here is very much alive.” Gunnell’s most recent surveys on Icelandic superstitions found that around half of respondents believe in the existence of elves and huldufólk (hidden people).

As I explored, I made sure to stick to Krafla’s wooden walkways, which do more than protect hikers’ feet from the scalding earth. The site itself needs protection: knotted lava formations lose shape underfoot and their delicate lichen coverings wear away. In a place where huldufólk are thought to punish those who harm the land, I thought it smart to adhere to well-trodden paths.

Nearly 18km south of Krafla, the scenery is more sinister still. Translating to “dark castles”, the Dimmuborgir lava fields have the appearance of a goblin kingdom: granite pillars sprout from the ground and underground caverns bulge beneath your feet. Most striking is Dimmuborgir’s Kirkjan (church), which resembles the pointed arch of a Gothic church doorway. The charred archway surrounded by mounds of volcanic rubble formed naturally 2,300 years ago, as lava cooled and collapsed over marshlands.

Geological researcher Oddur Sigurðsson documented and photographed the region during the Krafla fires, from 1975 to 1984. Surveying both Krafla and surrounding areas such as Dimmuborgir, he watched lava fountains blast out from the caldera and measured seismic swarms shaking the earth for a distance of 80km. Contoured pahoehoe lava crusted over as new earth within a day of billowing from the Earth’s mantle. And yet all this dramatic change was part of an ongoing churn for Iceland, an island endlessly renewing through volcanic activity.

“A newcomer to the region today will not experience the landscape in a different way from a traveller half a century ago,” Sigurðsson said. “The Krafla fires were only one episode in a never-ending geological process.”

To outsiders, lava fields like Krafla and Dimmuborgir have an apocalyptic feel. But to Sigurðsson, theres a splendour amid all the drama and peril. “I was amazed by how fast moss could grow in a new volcanic crater,” Sigurðsson said. “Never before or since have I encountered such wild thyme blossom.”

After Iceland’s mortal realm heals from the abyssal rumbles, new life quickens once again.