HVERADALIR INFORMATION PANELS
THE HIGH TEMPERATURE AREA IN HVERADALIR
Hveradalir is a grassy basin on the southwest side of mountain Stora-Reykjafell, which is on the south side of Hengill volcano. Stora-Reykjafell is an old crater formed by a steam-blast (phreatic) eruption during the Ice Age, with its tuff slopes. The centre of this ancient explosion crater is named Stóridalur. The hot springs area in Hveradalir is part of the hot springs area of Heillisheidi, which is one of many high temperature areas in the Hengill zone.
Hengill volcanic system lies in the far eastern part of a row of five volcanic systems on the Reykjanes Peninsula. The volcanic zones are clearly lined up along specific fissures which lie in the NE-SW direction over the whole peninsula. The Reykjanes volcanic zone is one of the most active volcanic areas in the country. The Hengill volcanic system is quite different from the others in that it is the only central volcano on the peninsula, with its own magma chamber and its acidic eruptive activity.
Hengill is an active central volcano and its volcanic fissure system lies from Selvogur on the Reykjanes peninsula in the southwest and stretches over 50 to 60 km northeast of Þingvallavatn lake. The volcanic system is about 5 to 10 km wide. The widest part is at Þingvallavatn lake, but narrows to the southwest.
The volcanic system covers about 100 km2 and one of the largest high temperature areas is to be found there. The volcanic system consists of three central volcanoes: Hveragerdi – Graendalur, which is the oldest one (300.000-700.000 years old); Hromundartindur (younger than 115.000 years) and Hengill, which is still active today.
Three eruptions due to Hengill volcanic activity are known to have occurred in Holocene time (last 10.000 years). The last one about 2000 years ago.
BOREHOLES AND THE LAGOON
In 1986 a 50 m deep hole was bored by the side of the ski lodge at Hveradalir. The aim of the boring was to explore whether it would be possible to make use of geothermal heat for house heating. Another 100 m deep hole was then bored in 1993 and is to be seen here to the south of the path. Nowadays, hot water is used to heat up the ski lodge.
The lagoon bridged by the path, is man-made. It receives the runoff from the hot springs area. Deposits seen in the water are formed when minerals, silicon especially, precipitate when spring water comes up to the ground surface and cools down.
WHAT IS A HIGH TEMPERATURE AREA?
There are about 20 high temperature areas in Iceland. They are all situated on or near active volcanic and rift zones.
They are often situated in the centre of volcanic systems and are defined as areas where geothermal temperature is 200°C at 1000 m depth. For the geothermal fluid to reach this temperature, the source of heat must come either from a shallow magma chamber or from a magma intrusion, where the magma heat can reach 1000-1200°C.
When groundwater is heated, its density changes. Gases released from the hot magma mix with the groundwater and reach the surface as a low-density acidic geothermal water or steam. The gases can be hydrogen sulphide (H2S) which causes the stench, sulphur dioxide (SO2) and carbon dioxide (CO2).
On its way to the surface, this hot and acidic geothermal fluid boils the sedimentary strata. This causes chemical reactions between water and rock, releasing minerals.
Hot geothermal water contains therefore a large amount of dissolved substances, such as silicon, lime, sulphur, and more.
In the hot spring area at Hveradalir you can find both fumaroles and hot mud pools. A hot stream flows through the area, so the groundwater level of the high temperature area is rather high, but still variable.
The water level of the lagoon fluctuates according to the groundwater level of the area. Sometimes there is a lagoon here, sometimes it is all dry as bone.
The groundwater level of the high temperature area depends on precipitation and thaw, but high temperature water that comes from underneath Hengill is originated from the Langjokull glacier, wherefrom it flows as groundwater first into Þingvallavatn Lake, thence under Hengill.
THE HORTICULTURAL FARM AT HVERADALIR
heat. That greenhouse was part of a horticultural farm which the couple Anders C. Höyer and Erica Hartmann from Latvia started to build up in 1927. The previous year Anders had helped with the building of the first horticultural farm in Iceland where greenhouse production was made possible, named Blómvangur at Mosfellsbaer.
Icelandic farmers had used naturally heated soil for a long time to grow potatoes and other vegetables before greenhouse production using geothermal heat came into being in the early 20th century. But this new way greatly facilitated cultivation.
Anders, who was an enthusiastic journalist about horticulture, had just arrived in Iceland when he got permission to settle at Hveradalir with his wife, who had moved to Iceland from Latvia that summer. They moved up to the heath the next autumn and lived in a tent until they had built the farm, which was heated with geothermal heat. They got married at the farm in the presence of the Danish ambassador, on 27th October 1927. Life was not easy, at least in the beginning, but the couple quickly established a shelter, which enabled them to develop further structures and thus secure their livelihood.
In the greenhouse they first grew begonias, but after the enlargement of the greenhouse in 1929, they began growing roses in flowerpots. They also hunted ptarmigan and brew beer out of Icelandic plants to sell to travellers, as well as offering mud baths. They also sold their products on markets in Reykjavík.
The Reykjavík Ski Association built a cabin next to the couple’s farm in 1934 and started selling refreshments. The proximity of the cabin pushed them to move away to Gunnuhver at Reykjanes, where they tried to pursue similar activities as at Hveradalir, until they moved to Denmark in 1937. After World War II they moved back to Iceland where they lived to the end of their lives
The couple’s life at Hveradalir seems to have been fulfilling, as Erica said when looking over her life: “I wish we had never left Hveradalir”.
The buildings stood on the slope on the north side of the path and you should be able to see the ruins.
References: Sigurðsson, Haraldur, Hallir gróðurs háar rísa, Icelandic Association of Horticulture Producers, 1995.
TYPES OF HOT SPRINGS IN HIGH-TEMPERATURE AREAS
The main surface features of high-temperature areas include a diverse range of steam vents and mud pools. The ground is often highly altered, with vivid colors caused by dissolved geothermal minerals. In some high-temperature areas where the groundwater level is high, geysers can also be found.
The large hot spring located north of the walking path is a mud pool. Here, geothermal steam rises to the surface, and the acidic fluid has dissolved the surrounding rock, transforming it into mud. The mud boils and bubbles, splashing onto the edges of the pool and forming a grayish coating. The gray color of the mud is usually due to tiny crystals of pyrite (FeS).
Mud pools form where the rock has broken down due to chemical weathering from acidic geothermal steam. For these features to develop, there must be a sufficient amount of surface water or condensed steam. The mud consists of water and boiled, altered rock, and its thickness depends on the availability of surface water.
Steam vents are also present in the area. These form where the groundwater of geothermal systems is so deep that only steam or gas reaches the surface. The temperature in such steam vents can exceed 100°C at the surface. The steam released in high-temperature areas consists mainly of carbon dioxide, hydrogen, and hydrogen sulfide.
Hot springs are found where steam has mixed with surface water.
THE FIRST HOT SPRING STEAM BATH
Vísir (newspaper) on 27th October 1938:
“Healing power of the spring steam and of the spring mud. Could Iceland possess unused health wells? - The steam baths at the ski cabin at Hveradalir and hosts’ stays at Hveragerdi ...”
“Those, who have been on their way east over the heath of Hellisheidi, have probably noticed a small hut that has been built just above the ruins of Höyers’ house at Hveradalir. Over the hut and around vapour is sent out by the sulphur hot spring, but pipes lie from the spring itself into the house and then out again. This seems to be the first bathhouse in Iceland, where only spring steam is used to warm up and bathe people. This is a novelty, which deserves full attention, especially for Reykjavík residents, since they live nearby and can easily enjoy the baths, in particular our great skiers who practice their sport there during most winter.” (...)
“Inside the house, you see first a changing room. There are benches, where you can lie and receive a massage for health and refreshment, whether you are an athlete or a patient...” (...) “From the changing room there is a passage to the bath compartment, where there is a cold shower, as part of the steam bath program and necessary to fully enjoy the bath that follows. In the innermost part of the house is the bath compartment itself. It is not big, but large enough for several people to bathe at the same time. The pipes lie from the spring through the compartment and are equipped with a handle, so you can with one grasp open for the steam flow, fully close or regulate at will. Sveinn Steindorsson from Asum at Hveragerdi has built this bath hut and arranged all the equipments neatly as described above.” (...)
If a stay at geothermal areas proves to be as salutary as some tell it to be, then with more experience we should be able to provide the required conditions to move forward and who knows whether Iceland could not become an option as a health resort for foreigners, which could bring relief to most of them and thus make it easier to run the place than before.”
DISSOLVED SUBSTANCES IN GEOTHERMAL FLUIDS
As water circulates through geothermal systems, chemical interactions occur between the rock and water when the hot and acidic geothermal fluid flows through the bedrock. This process results in a large amount of dissolved minerals being carried to the surface with the hot fluid. However, when the water reaches the surface, it cools down and pressure decreases. As a result, the water becomes saturated with minerals, which then precipitate out.
During the upflow of geothermal fluid and steam, surface alteration occurs, primarily due to the boiling of rock in a sulfuric acid-rich environment. This alteration causes primary minerals and volcanic glass in the rock to dissolve, transforming into secondary minerals. Some of these minerals remain and reorganize into alteration minerals that are in equilibrium with the prevailing temperature and acidity levels. This process leads to the formation of new minerals at the surface of high-temperature areas, mainly clay minerals, which appear as white, gray, yellow, or red clay deposits.
THE VIVID COLORS OF HIGH-TEMPERATURE AREAS
Mud in high-temperature areas can appear in various shades. The most prominent colors include the yellow of sulfur (S), the red of the mineral hematite (iron oxide, Fe₂O₃), and the dark gray of mud, which is usually caused by tiny crystals of pyrite (FeS). Gypsum (calcium sulfate, CaSO₄) is easily recognizable and forms white, matte crystals. Gypsum can also exhibit other colors, such as reddish hues due to hematite or even a greenish tint from copper, though this is rare.
