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According to geological studies, the formation of the Great Geyser goes back to the final period of the ice age.
In other words, the hot springs have existed for over 10000 years. In this relatively long period, the activity of the Geyser has changed and varied. How nature will form the future of the Geyser, Strokkur and the other thermal wonders is unknown. The first written record of this thermal area can be found in 1294 when an earthquake caused major changes. Earthquakes, in general, influence the behaviour of geysers. For example, the great earthquake of 1630 woke the geysers from a 40 year resting period causing such a massive reaction that renewed earthquakes occurred.
The height of the fountains varies constantly, a phenomenon mainly due to earthquake activity. Before the most recently occurring earthquake in 1896, the Great Geyser was calm, but the fountains from the Strokkur spouted up to a height of 60 meters. The Geyser has risen to 100 meters at its best. It seems odd that such a natural phenomenon can be owned by someone, but in actuality the thermal field has changed owners several times in its history. Until 1894 it was part of the nearby farm Laug. Its occupants sold it then to James Craig, who later became Minister to North Ireland. During this period, visitors were charged an entry fee. After further changes in ownership, Sigurdur Jonasson bought the thermal field and gave it as a gift to the people of Iceland. A special Geyser committee was formed to the purpose of setting up an enclosure and protecting the vegetation from sheep.
The oldest accounts of the Great Geysir are from the year 1294.
Large earthquakes shook the southern lowlands of Iceland and the thermal area in Haukadalur valley changed to a large extent. In written annals tales report that "large hot springs" were formed, now thought to indicate that the hot springs started to spout. The fame of the area increased in the following centuries, and especially that of the Geysir itself. This was not surprising as erupting geysers were at the time not known in Europe outside Iceland. During the centuries after 1294 the intensity of the thermal ares apparently increased after large earthquakes, striking on average every 100 years. The geothermal area which is named after the famous Great Geysir is a high temperature geothermal area. This term is used over geothermal systems that are within the zone of active rifting and volcanism, and the temperature in the subsurface system is higher than 200°C at less than 1 km depth.
The Geysir thermal ares is one of the smallest in Iceland, covering some 3 km2 at the surface. The thermal ares is at the eastern margin of the western volcanic zone, and differs from other high temperature areas in that no volcanic activity has been in the area during the last 10.000 years (in Holocene). Studies on the chemistry of the water in the hot springs indicates a subsurface temperature near 240°C, i.e. in the geothermal system at a depth of 1 km or more.
The hot springs in the Geysir area are of different types. Geysir and the hot springs to the west and south are normal hot springs, i.e. they emit hot water ascending through narrow channels from deep sources in the crust. The temperature of the hot springs is up to 100°C and some are constantly boiling - if the temperature at depth rises above boiling the hot springs erupt which means that they are geysers. The word geyser is derived from the name of the famours Geysir. North of Geysir are fumaroles, a type of geothermal where only steam and gas escapes from the geothermal system. At the fumaroles one can sometimes observe bright yellow spots or stains; this is native sulphur, crystallizing from the steam. It is the suphur (H2S) which also gives the rather unpleasant smell in such areas - it is not your friend! The southern part of the thermal area at Geysir is named Thykkuhverir - i.e. the "viscous hot springs" - indicating mud pots. The type named mud pots are actually fumaroles that are boiling up through suface water or the groundwater and during dry spells these can change into steaming fumaoles, instead of bubling hot mud. These mud pots are often around 70-80°C and can be dangerous as the eat the subsurface around and can make hollow chambers just under the surface.
The geysers are one type of the hot springs, but such features are very rare in the world - not existing in Europe outside Iceland. This is the reason that for centuries geysers where only known in Iceland and travellers came from wide afar to inspect and admire them. Geysers erupt because the thermal water ascending throuh ther channels boils at some depth below the surface. As the water boils it flashes into steam, and as the steam occupies far greater volume than water the water above in the channel is thrown high up into the air. At about 23 m depth in the Geysir pipe the water is at 120°C temperature. It is in equilibrium with the pressuere of the water above in the pipe, i.e. the weight of the water above keeps the boiling down. At a depth of around 16 m, the temperature of the water sometimes rises above boiling, seen as increased turbulence at the surface.
This turbulence (boiling) can increase to the point where the water above in the pipe is lifted slightly, and a chain reaction starts - the pressure decreases making further boiling possible and the water flashes into steam, resulting in an eruption in Geysir. The boiling now extends down into the pipe, throwing more water into the air. When all the water in the pipe has been thrown away the water coming from depth changes immediately into steam and a steam eruption follows the water eruption, whith accompanying noise. The water-phase lasts for few minutes and the steam-phase considerably longer, graduately dying out and the cycle starts again. As the steam-phase dies out the water has drained the channels deep into the earth and it will take 8-10 hours for Geysir to regain its water.
Following large earthquakes in Souhtern Iceland the 17th and 21st June 2000 Geysir started to erupt after having been dormant since 1915. It was rewoken in 1935 and erupted then for several years, but then got back to sleep. Now it erupts every day, sometimes several times per day, but has not regained its former glory as the eruptions got up to 50-60 m. Now it erupts 8-10 m but does it intermittently for some time when it starts. The eruptions start as turbulence at the surface, then gushes of water are thrown 8-10 m into the air. As the erupting water falls back into the bowl it cools the water in the bowl and the boiling stops. The geyser Strokkur (churn) erupts every 8 minutes and has been the main geysir in the area since 1963, when its channel was thoroughly cleaned. Strokkur was formed in an earthquake in 1789 and was active until the next earthquake in 1896, then it was shut down by the quake.
Other geysers in the area are Sódi (the sod), Smiður (the carpenter), Fata (the bucket), Óþerrishola (the non-draught-hole, or the rainmaker), Litli Geysir (the small Geysir) and Litli Strokkur (the little Strokkur). These geysers now only erupt if treated with soap, except Óþerrishola which sometimes erupts if the air pressure gets low. In the earthquakes 17th and 21st June 2000 great changes could be seen in the thermal area. The hot spring Konungshver (the king's hot spring) and Blesi (the blazer) started to boil vigourusly, up to 0,5-1 m.
Óþerrishola and Fata also started to erupt, and Fata sometimes twice a day. Several new springs were born and the amount of water flowing from others icreased. Geysir was however the one most affected. For centuries the eruptions in Geysir were considered supernatural and many teories were built to explain these wonders. One of these ideas was that large subsurface caves were beneath the area, gradually filling with steam. When the steam escaped the water in the eruping pipe above was thrown into the air.
A German chemist, Robert Bunsen, came to Iceland in 1846 to inspect Geysir. He was the first one to realize that the eruptions were related to the overheating of the water at depth in the Geysir pipe and as the water flashed into steam the geyser erupted. One of the beauties of the Geysir area are the buff coloured silica sinter around the hot springs. The sinter is built over the centuries from silica (SiO2) depositing from the hot water as it cools. In old and eroded mountains one can inspect the old channels of the thermal water as white veins occupiyng cracs in the rock. he silica sinter is delicate and although constantly being formed it takes years, reminding us to respect the beauty of this unique area and leave the nature to evolve according to its own laws.
Dr. Helgi Torfason, geologist with the Natural History