Gunnuhver hot spring on Reykjanes peninsula

A geothermal system fed by the sea

The Reykjanes geothermal system differs from many of Iceland’s other high-temperature areas because much of the water circulating deep underground is derived from seawater.

Seawater penetrates fractures in the volcanic bedrock and circulates downward, where it is heated by the geothermal system. As it moves through the basalt, the water reacts chemically with the surrounding rock before rising again through fractures and faults.

At the surface, steam and geothermal gases mix with groundwater. Gases such as carbon dioxide and hydrogen sulphide contribute to making the water acidic, gradually altering the volcanic rock into clay.

That process is what creates the mud pools at Gunnuhver. The largest is approximately 20 metres across and boils vigorously within a rim of altered clay. Unlike a clear hot spring, the water is mixed with fine clay particles produced by geothermal alteration, giving the pool its thick grey appearance.

The geothermal landscape is not static. Pressure, temperature and groundwater conditions beneath the surface change, so visible activity can shift from one part of the field to another.

A particularly noticeable change occurred in 2006, when electricity production began in the nearby Reykjanes geothermal field. Withdrawal of geothermal fluid lowered pressure within the reservoir, and surface steaming in the area increased significantly.

The resulting period of stronger geothermal activity damaged some of the road and walking infrastructure then in place. New walkways and viewing platforms were later constructed, allowing visitors to experience the field without walking directly onto active geothermal ground.

Visiting Gunnuhver

Gunnuhver is reached from Road 425 on the western Reykjanes Peninsula, close to Reykjanesviti lighthouse. Parking is available beside the geothermal area, and wooden walkways lead towards the viewing points.

There are two principal viewpoints. One lies close to Gunnuhver itself, where the scale, sound and movement of the mud pool are most apparent. From there, you can look down into the active area and hear the constant hissing and boiling of the geothermal system.

The second viewpoint is on Kísilhól, a nearby silica-covered hill. From there, the perspective is wider and gives a better sense of Gunnuhver within the surrounding geothermal field rather than focusing only on the main pool.

The present walkways and viewing areas provide wheelchair access. Visitors should remain on the marked paths, boardwalks and inside the fenced viewing areas because the ground outside them is active and unstable.

Wind direction can completely change the visit. On some days steam drifts away from the platforms and the mud pool is clearly visible. At other times the wind pushes dense steam directly across one viewpoint and hides almost everything.

When that happens, the other viewing area may give a much clearer view. Gunnuhver does not require a long visit, but it is worth seeing the field from both sides rather than stopping at the first platform.

The story of Gunna

Gunnuhver takes its name from Guðrún, usually called Gunna, whose ghost is said in local folklore to have haunted this part of Reykjanes.

According to the story, a man named Vilhjálmur lived at Kirkjuból in Suðurnes. Gunna was his neighbour and owed him money, but was unable to pay the debt. Vilhjálmur therefore took one of her cooking pots as security.

Some time later, Gunna came to Kirkjuból asking for something to drink. She appeared agitated and was offered consecrated wine, but according to the story she poured it away and instead drank a bucket of water before leaving.

When a man who lived with her returned home from fishing later that day, he found Gunna dead in her bed. A coffin was made, and her body was taken towards Útskálakirkja for burial.

Those carrying the coffin were said to have noticed that it seemed strangely light. Later, while the grave was being prepared, Gunna was reportedly seen among the seaweed at Útskálar and declared that there was no reason to dig deeply because she would not remain in the grave for long.

After that, stories of hauntings began spreading across the area.

Vilhjálmur later attended a gathering at Útskálar and stayed late into the evening. Although he was offered company for the journey home, he refused and never reached Kirkjuból.

The following day he was found badly beaten at Hrossalág. He was taken back to Kirkjuból but died soon afterwards, and Gunna was blamed.

According to the story, her ghost continued causing trouble, entering houses, frightening livestock and making life increasingly difficult for people living in the area.

Eventually two men were sent across the peninsula to seek help from Séra Eiríkur Magnússon of Vogsósar, a clergyman who appears in a number of Icelandic folk stories as a man capable of dealing with supernatural problems.

Eiríkur gave the men a knotted object and instructed them to deliver it to Gunna. When she received it and began unravelling the knots, she reportedly realised who had sent it.

The story gives her words as essentially: “I expected the devil, but not the man from Vogsósar.”

The knot then began moving across Reykjanes and Gunna followed it. It led her over the peninsula until it reached the edge of a boiling hot spring, where she followed too closely and fell in.

From that point onward, according to the story, the spring became known as Gunnuhver — Gunna’s hot spring. The steam rising from the ground later became part of the legend as well, with people saying that Gunna could still sometimes be seen struggling within the mist.

• Gunnuhver is generally described as Iceland’s largest mud pool, approximately 20 metres across.
• The Reykjanes geothermal system is largely recharged by seawater rather than only freshwater.
• Acidic geothermal fluids alter volcanic rock into clay, helping create Gunnuhver’s mud pools.
• Geothermal activity at the surface increased noticeably after electricity production began in the Reykjanes geothermal field in 2006.
• Gunnuhver takes its name from Gunna, a ghost in local folklore.
• Séra Eiríkur Magnússon of Vogsósar is the figure traditionally credited with finally dealing with Gunna.
• Two main viewing areas give different perspectives over the geothermal field: one beside Gunnuhver and another on Kísilhól.
• Wind direction can determine whether the main pool is clearly visible or hidden completely by steam.