Icelands "Strokkur Geysir" is one of the most persistent geysers in the world and lies in the Haukadalur valley at the base of Laugarfjall hill about 50 m from the site of the famous, but rarely active, "Geysir" which is the source of the generic name given to these kind of hot springs. The term Geysir (Engl. Geyser) is itself derived from the icelandic word "geysa" which means to gush. The small geothermal area in which the geyser lies is one of the major tourist attractions in iceland. Strokkur was first reported in 1789, after an earthquake which probably created or unblocked its conduit. Eruptions were regular until 1896, after which a renewed earthquake inactivated the geyser. In 1963, local people succeeded in unblocking the plumbing system and Strokkur has been active ever since. First records of geyser activity in the area date back to 1294, when the great Geysir is thought to have become active Eruptions usually occur with intervals of between 5-10 minutes and involve a single burst reaching a height of up to 30 meters, although occasionally up to 5 bursts in relatively quick succession are observed. Prior to eruptions, the pool is full and gently pulsates up and down. The eruption commences when a pulse of steam rising from below pushes the water in the pool upwards forming a large dome (or bubble) of water through which the steam bursts and expells much of the water in the pool skywards. After regular eruptions the pool is empty but becomes rapidly refilled by flowback and water rising from underneath. Following smaller irregular eruptions which are also frequently observed, the pool may remain almost full and renewed activity may occur very rapidly: a few seconds only;