A geyser is a thermal spring spring that regularly hurls its water out. This phenomenon was named after the Great Geyser in Iceland. The geyser is a special type of thermal bath (hot spring), which is one of the volcanic aftermaths with the gas or steam emitting fumaroles, solfataras and mofets. All of these manifestations in the aftermath of volcanism are abundant in Iceland.
The geyser – a thermal spring
A hot spring in young volcanic areas that regularly emits its water like a fountain is called a ” geyser “. It is fed by warm groundwater and consists of a deep chimney that merges into a basin on the surface. The name goes back to the “Stóri Geyser” (Great Geyser), which is located in the geothermal field of Haukadalur approx. 80 km northeast of Reykjavik on Iceland (Iceland. “Geysa” = wild flow). “Geyser” became the generic term for all spring springs in the world.
The Great Geyser threw up a 30 to 60 m high (even 110 m was reported) column of water every 24 to 30 hours. After initial subterranean rumblings and small explosions, a sheaf of boiling hot water jets accompanied by clouds of steam shot up from a rock tube with a whirring hiss, which formed a fantastic dream figure, only to collapse after a few minutes and leave a silent well.
The riser pipe is about 3 m wide and 30 m vertically into the depth. It is located in the middle of a well basin with a diameter of 18 m. This geyser has been known for centuries. Its age is estimated at 10,000 years. The regular emission periods have changed again and again (1772 every half hour, 1883 every twenty days, 1905 every three to eight days). In the middle of the 20th century, tectonic processes caused the activity to stop (Fig. 1). Against the protest of the Icelanders, an eruption from a height of 50 m was caused again with the help of 40 kg of soap for a film production. However, a certain revival has now occurred due to the younger Vulkanisnus.
However, visitors to the Naukadalur National Park do not lose sight of a natural hot water fountain. A similarly beautiful experience is offered by Strokkur (= butter churn), only 150 m away, whose fountain shoots 20 to 40 m high every 5 to 10 minutes (Fig. 2). After the water has flowed back into the gullet and this has been filled with groundwater, the spring remains quiet for a while; only individual vapor bubbles pearl up to the surface. Then, without prior notice, the water begins to billow, bulges like a bell, and finally steam bubbles rise explosively from the ground and pull the water at the edge with them. The water in the 5 m wide geyser basin has a temperature of 97 °C.
The thermal water usually contains many different minerals, which are deposited around the pool after the water has evaporated and form the sintered terraces.
In this thermal area there are numerous other quiet hot springs, small lakes with turquoise water, surrounded by sintered terraces.
The geyser phenomenon was first explained by ROBERT BUNSEN in 1846. The geyser is supplied with more heat in the depth than can be given off through the narrowed source tube. This causes the water to overheat and its temperature to rise to more than 100 °C. The pressure of the water column above it increases the boiling point. Therefore, the water must generate a higher pressure than the loading pressure if it is to erupt. Numerous rising vapor bubbles lead to a sudden pressure relief of the water mass and lower the boiling point. In the event of an explosive ejection, the water immediately turns into steam.
The geyser is a special type of thermal bath (Greek = ‘warmth’), the thermal springs with over 20 °C, which because of the minerals dissolved in them usually have a healing effect (healing springs). With other geothermal phenomena (fumaroles, solfatars, mofets) they belong to the volcanic aftermath (Fig. 3).
Geysers are known about 30 in Iceland. Worldwide reference should be made in particular to the USA (Yellowstone National Park) and New Zealand (Rotorua on the North Island).
Thermal baths, on the other hand, are widespread and, in addition to water power, form the island’s decisive energy potential.
The capital Reykjavik z. B. is completely supplied with thermal energy from thermal baths. Thermal water is pumped up from the underground of the city and its surroundings (partly also brought in by pipelines from distant geothermal areas; Fig. 4). The boreholes are between 628 and 2850 m deep, the temperature of the water is 86/87 °C. In the “Perla”, in tanks clad as a modern building on the Öskjuhlid (ash hill), the thermal water is stored in order to be distributed over the city like a water tower. Hence, Reykjavik has absolutely smokeless, clean air. The Perla’s roof terrace is also a popular vantage point with good foresight.
Other important thermal baths are located in the geothermal fields of Landmannalaugar, 30 km east of the Hekla, and Hveravellir on the Kölur inland route between Langjökull and Hofsjökull.
Fumaroles emit volcanic gases with temperatures of 800 to 2000 °C. When the temperature drops, the proportion of sulfur dioxide increases in them (Fig. 5). This gas gives off an annoying and pungent odor. Fumaroles occur mostly in association with solfataras, which consist mainly of water vapor with a small amount of sulfur dioxide and carbon dioxide and have temperatures of 200 to 1000 °C.
The best example of both types of volcanic after-effects is the geothermal area of Hverarönd on Nàmafjall northeast of the Myvatn (Mosquito Lake) in northern Iceland. In addition to the hissing gas and steam, you can also observe boilers with bubbling, boiling bluish-gray mud, over which clouds of steam dance. There are also spring pools with clear water. They can also be observed 8 km north on the Viti der Krafla. The scenery at Námafjall is dominated by the reddish brown of the soil, the light yellow of the precipitated sulfur, the white of the gypsum efflorescence (Fig. 6) and the various green of the water.
Mofettes are cool carbon dioxide spills that are less common.