This most famous and former largest spouting hot spring of the world probably was created during an extended earthquake period at the end of the 13^th 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. Silica deposits have created a mound around Geysir and its bowl measures about 18 metres across. The main natural shaft of the spring is 18 m deep and 2 m across.

For centuries on end, Geysir erupted and attracted tourists, but after the turn of the 19^th century its activity diminished and after 1916 it has been very irregular. Scientists concluded that its cooling surface was too large and reduced it in size with good results for a spell. The highest measured eruptions reached over 80 m and before it erupted it rumbled and small tremors were felt. The hot spring area surrounding Geysir is about 500 m long and 100 m wide.

The ancient silica deposits cover a much larger area, close to 200 thousand square meters, which confirms the existence of a much larger hot spring area in the past. There are dozens of hot springs within the present active area and some of them spout as Geysir did. The most prominent one is Strokkur (The Churn), which spouts at intervals of 3-5 minutes. The hot spring area is fenced off and was declared inviolate in 1953.