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Deildartunguhver - geyser in Europe's most powerful hot spring
Deildartunguhver – geyser in Europe’s most powerful hot spring. / Bernd Thaller, Flickr / CC BY 2.0

WorldBlue  In short

The largest spring in Iceland is Deildartunguhver – constantly boiling pool of geysers and spouters. This might be the most powerful thermal spring in the world. And… one more record: here starts the longest district heating system in the world!

3.7 out of 10 stars 37.3%

GPS coordinates
64.6636 N 21.4107 W
Location, address
Europe, Iceland, Western Region (Vesturland), some 7 km west from Reykholt, at Krauma Spa, in Reykholtsdalur valley
Thermal springs, Geysers, Ecosystems
Alternate names
Tunguhver (in older sources)
Up to 3 m
Average discharge
180 l/s

Map of the site

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WorldYellow In detail

Geysers and hot springs

Deildartunguhver is named after Deildartunga – a nearby farm that has been mentioned already in the Icelandic medieval sources. This was valuable agricultural land long before the use of geothermal energy started. The fate of the legendary Snorri Sturluson (1179-1241) is linked to this site as well.

Deildartunguhver is located in the Reykholt geothermal area. This area of thermal water includes one more unique landmark: the nearby Árhver geysers in the middle of a river.

Springs emanate at the foot of Hverahóll hill and have at least nine vents. The temperature of the water at the surface here is 95 – 97 °C. A little deeper it is above the boiling point.

Steam around Deildartunguhver
Steam around Deildartunguhver. / Reykholt, Wikimedia Commons / CC BY-SA 3.0

Some of the spring vents behave as water spouters and even geysers. The most active ones can erupt up to 3 m high. In 1810 the geysers were taller – up to 4 m – as described by Scottish geologist Sir George S. Mackenzie.

Deildartunguhver almost continuously is shrouded in dense steam. Thus it is hard to find a moment to take a clear picture of the springs.

District heating system

In the 1970ies, during the oil crisis, a dire need for cheaper energy arose. As a result, a very ambitious project was realized around 1979: there was built a district heating system between Deildartunguhver and the coastal towns – Borgarnes and Akranes. The pipe to Akranes is 64 km long. Water at the end of this pipe still is very hot: 78 – 80 °C.

Later there were found other sources of geothermal energy nearer to the towns – but too late, the system was built and functional.

Here the water from Deildartunguhver starts a path in world's longest district heating system
Here the water from Deildartunguhver starts a path in world’s longest district heating system. / bowlingbal, Wikimedia Commons / CC BY-SA 3.0

Thus, the visitors of the site can see how twisted can be the compromise between nature conservation and development. Deildartunguhver is a protected monument of nature. But, as the water appears above the ground and flows for some meters, nature conservation ends: water reaches a system of concrete gutters and disappears in pipes.

The only endemic plant in Iceland

These few meters of “freedom” though are very important. Around the hot springs grows a unique plant, which is found only here: the fern Struthiopteris fallax. In 2019 this small plant (2-5 cm long leaves) was confirmed to be a separate species. This is the only unique species of plants in Iceland.

Struthiopteris fallax - fer which grows only at Deildartunguhver
Struthiopteris fallax – fer which grows only at Deildartunguhver. / Ragnhild&Neil Crawford, Wikimedia Commons / CC BY-SA 2.0

One more important find is thale cress (Arabidopsis thaliana) – the only find of this plant in Iceland.


  1. Dirk Niemann, Deildartunga / Reykholt, Volcanic Springs. Accessed on June 2, 2019.
  2. Sonia Molino, Jose M. Gabriel y Galán, Pawel Wasowicz, Pablo de la Fuente, Emily B. Sessa, The Struthiopteris spicant (Blechnaceae, Polypodiopsida) complex in Western Europe, with proposals for taxonomic and nomenclatural changes, Plant Systematics and Evolution (2019) 305:255–268. Accessed on June 3, 2019.

Deildartunguhver is included in the following article:

WorldYellow Linked articles

Gullfoss, Iceland
Gullfoss / WoSie, Wikimedia Commons / CC-BY-2.5.

Wonders of Iceland

Iceland is very rich with peculiar natural landmarks and the island contains also interesting cultural landmarks. The highlights of Iceland are the magnificent waterfalls as well as geysers and other geothermal features.

Geysir and Strokkur erupting simultaneously, June 1984
Geysir and Strokkur erupting simultaneously, June 1984 / Roger Goodman, Flickr.CC BY-SA 2.0.


Hasty hydrogeologists would say: geysers are thermodynamically and hydrodynamically unstable hot springs. “Normal” people would say – geysers are hot springs that at more or less regular intervals shoot up a fountain of boiling water and steam. Sometimes these fountains are even 100 m tall… or even 450 m!

Three Sisters Springs, Florida
Three Sisters Springs / corvettediver, / CC BY-SA 2.0


Powerful natural freshwater springs belong to the most fascinating monuments of nature. Even more exciting is the diversity of unusual springs – mineral springs, hot springs, submarine springs as well as the unusual black smokers. Especially beautiful are such natural rarities as travertine, silica, or salt terraces created by warm and hot springs and, especially, geysers.

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The Glorious Geology of Iceland’s Golden Circle

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