Located in the Þingvallavatn Lake in the Þingvellir National Park in Iceland, Silfra is crevice between the North American and Eurasian plates.
The geology of Silfra and the Þingvellir valley are connected to the tectonic drift of the Eurasian and the North American plates. Every year, the plates drift about 2 cm apart, which builds up tension between the plates and the earth mass above. This tension is released through a major earthquake approximately every ten years. In these earthquakes, cracks and fissures are formed in Þingvellir. Silfra is one of the largest cracks and started with a deep cave where most of the underwater wells nourish it. [x]