[4] Geysir lies in the Haukadalur valley on the slopes of Laugarfjall lava dome, which is also the home to Strokkur geyser about 50 metres (160 ft) to the south.

[6] The name "Geysir" was first mentioned in written sources in 1647;[9] as unusual natural phenomena were of great interest during the Age of Enlightenment, the term became popular and has been used for similar hydrothermal features worldwide since then.

[4] In 1811 George Mackenzie, a geologist, first proposed that expansion of steam in a subsurface cavity explained Geysir's activity.

[citation needed] In 1846, research on Geysir, and Iceland sponsored by the Danish Crown, by amongst others, the German chemist Robert Bunsen, resulted in a better general explanation of the mechanism of geyser activity which contributed significantly to the more refined models used today.

[12] The records of recent centuries show that earthquakes have tended to revive the activity of Geysir, which then subsided again in the following years.

[19] A current geological definition of a hot water geyser is "…a hot spring characterized by intermittent discharge of water ejected turbulently and accompanied by a vapor phase"[9] which is a technical correction on historic definitions that mentions steam and a column in air.

[22] As it is closer to sea level than most of the world's 1000 odd geysers the actual erupted water temperature is higher than most.

[25] Geysir is on the eastern slopes of the rhyolitic Laugarfjall lava dome,[26] but the hyaloclastite nature of the rock that the water erupts through, may be important in its fracture network.

[29] Once Geysir became active, precipitation of opal from the geothermal water lead to a siliceous sinter apron around the geyser.

[14] Due to its eruption frequency, online photos and videos of Strokkur are regularly mislabelled as depicting Geysir.

[34] In that year the area was sold to James Craig (later Lord Craigavon), a whiskey distiller from Ulster and a future Prime Minister of Northern Ireland.

[34][35] Initially, he erected large fences around the site and an entrance fee was charged for visitors wishing to view the geysers.

[35] In 1935, he sold the site to film director Sigurður Jónasson who subsequently donated it to the Icelandic people in perpetuity,[34] although full public ownership of all routes of access did not take place until 2017.