Strokkur is part of a geothermally active site, with various mud pools, algal deposits and other geysers beside and around it such as Geysir. Strokkur has a long history of activity, beginning in 1789, after an earthquake unblocked the plumbing system of the geyser. It continued to erupt until 1896, when another earthquake blocked the conduit of the geyser. Then in 1963, locals cleaned out the blocked conduit and the geyser has been regularly erupting ever since. Strokkur and its surrounding areas, as mentioned is famous throughout Iceland and regularly attracts tourists to view the geyser, as it is one of very few natural geysers to erupt frequently and reliably.
Sequence of eruptions Water at a depth of 23 metres is around 120°C, 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, some of the water may be above boiling point, and this sets off the chain reaction we see. 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 & steam that forms the eruption. (from wikipedia, the free encyclopedia)