Strokkur is the most active sprouting hot spring in the Haukadalur Valley – home of the famous Geysir. These sprouting hot springs are probably was created during an extended earthquake period at the end of the 13th century. According to one of the annals, two large hot springs were created in the Haukadalur Valley in 1274, and many were ruined and disappeared.
As Geysir´s activities diminished, Strokkur (The Churn) has become the areas most popular attraction, spouting at intervals of 3-5 minutes. The hot spring area is fenced off and was declared inviolate in 1953.
Temperature on the surface of Strokk varies greatly, changing the wind and temperature of the environment. At a depth of 1 m the temperature is about 90-95 ° C and the water is heated down the shaft. When measured at Strokki on June 9, 2000 it was possible to measure down to 23 m depth. When the water is cooled in water, it becomes very heavy and sinks, resulting in currents at the top of the springs. Temperature, however, rises continuously down the course of each and is at 112 ° C at 10 m depth and at a depth of 23 m, the water temperature is around 130 ° C. Infusion of water at the bottom of the shaft pushes water upwards and a cold water vein enters a depth of 13 m cooling the water for about 10 ° C.
The water reaches a boiling pont higher in the shaft, creating a large air bubble just before eruption. The eruption occurs when water just below the air bubble is pervaded by the continuous flow of hot water right at boiling point and pressure. If water boils further down the shaft the eruption would be more powerful, as happens in Geysir. It does not happen in Strokki, but he fills up quickly, but Geysir could spend about 12 hours filling water after an eruption.
Photo Credit: CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=542345