Although the chronicles mention hot springs here already in 1294, the placename Geysir first appears in written sources in 18th century. This name comes from Old Norse "geysa" - to gush, to rush forth. This periodically erupting spring was such an unusual phenomenon for surprised Europeans that many did not believe that something like this can exist.
This landmark caused a flow of tourists to the remote Iceland. People of the Age of Enlightenment were searching for the explanation of the nature of geyser. George Mackenzie considered that geyser is powered by a steam, which is accumulated in some underground voids. The mechanism of geyser activity was discovered by the great German scientist Robert Bunsen in 1846 after he researched Geysir for 11 days.
History of activity
Analysis of sinter sediments around Geysir shows that this geyser is active approximately 10,000 years.
Earthquakes in this part of Iceland are frequent and one - two times per century here take place strong earthquakes.
The geyser activity after these events is changing. Geysir is a graphic example to this.
In 1630 after such earthquake Geysir started very powerful eruptions - whole area trembled during these eruptions.
In the first half of 19th century Geysir was renowned tourist attraction and it was erupting some 70 m high. Professor Bunsen estimated that in 1846 it was 43 - 54 m tall. Geysir was powerful also in the middle of 19th century.
Before 1896 Geysir declined in activity and months could pass between eruptions. The neighboring Strokkur in meanwhile increased in activity.
Earthquakes at the turn of 20th century revived Geysir - it erupted up to 60 m high, even once per hour.
In coming years the activity slowly decreased. Tourists wanted to see the spectacle and threw in the geyser stones and other objects. Initially it helped but finally Geyser got blocked.
In 1915 Geysir was dormant. In 1935 Geysir was reactivated when water level in its bowl was decreased by a ditch in the sinter rim. This was done by professor Trausti Einarsson and farmer Jón from Laug.
The measured height of Geysir eruptions in 1937 were up to 60 m.
In 1981 the ditch was cleaned again and geyser was activated by soap to make a movie. Now this is strictly forbidden.
After earthquakes in 17th and 21st June 2000 there were signs of activity - Geysir was erupting 8 - 10 m high. Since 2005 it again became weaker. In 2010 it erupted approximately once per day.
The giant hot spring
Geysir is by far the largest hot spring in Haukadalur. It is also the northernmost large hot spring in Haukadalur - with a group of fumaroles further north.
Upper part of Geysir plumbing system has been researched - it is an enormous bowl, lined with sinter. This bowl is 20 m in diameter, 1 m deep. In the centre of this bowl starts at least 23 m deep and approximately 1 m wide upflow channel - it becomes narrower at depth.
Now this geyser has low eruptions, but at its "good times" Geysir erupted for half an hour in several phases - after the first phase from the dried well suddenly bursted a very powerful fountain, sometimes reaching even 100 m height.
Now the temperature at the surface of spring is 73° C, but in 23 m depth - 120°C!
Water of Geysir contains the most of dissolved SiO2 in Haukadalur.
It is very possible that in future, after an earthquake Geysir will offer spectacular eruptions again.