Strokkur (Icelandic for "churn") is a fountain geyser in the geothermal area beside the Hvítá River in Iceland in the southwest part of the country, east of Reykjavik. It is one of Iceland's most famous geysers,[1] erupting about every 4-8 minutes 15 - 20 m high, sometimes up to 40 m high.[2]
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Strokkur is part of Haukadalur geothermal area, where are located various other geothermal features: mud pools, fumaroles, algal deposits, and other geysers beside and around it, such as Geysir.[3]
Strokkur was first mentioned in 1789, after an earthquake unblocked the conduit of the geyser. Its activity fluctuated in 19th century, in 1815 its height was estimated to be even 60 m.[2] It continued to erupt until the turn of 20th century, when another earthquake blocked the conduit again. In 1963, upon the advice of Geysir Committee locals cleaned out the blocked conduit through the bottom of the basin, and the geyser has been regularly erupting ever since.[3]
Strokkur and its surrounding areas regularly attracts tourists to view the geyser, as it is one of very few natural geysers to erupt frequently and reliably.[1]
Water at a depth of 23 metres (75 ft) is around 120 °C (248 °F), but cannot boil because of the weight of the water pushing down on it from above. When this water is forced up to around 16 metres (52 ft), some of the water may be above boiling point, which sets off the chain reaction: the pressure decrease allows more water to boil and flash boil into steam, which drives the unboiled water further up the conduit. As this happens closer and closer to the surface, with increasing velocity, the water and steam is forced out, and it is this mixture of water and steam that forms the eruption.[3]