Silfra is a rift formed in 1789, due to the movements of the two tectonic plates that frame Þingvellir National Park in Iceland. The North American and Eurasian plates, which run all the way through Iceland, separate at about 2 centimeters per year, and as they do, they tear open fissures in the land between them.
Scuba diving and snorkeling in Silfra is popular because of its clear water and location within the continental rift. There are three main dive sites: Silfra Hall, Silfra Cathedral and Silfra Lagoon. The Cathedral is a 100 metres (330 ft) long fissure with visibility almost from end to end. Shallow at the entry points and at the ends of the fissure, Silfra descends to a maximum depth of 63 metres (207 ft) but diving to this depth is seldom done as it requires technical diving skills. The water temperature is between 2–4 °C (36–39 °F) but can be comfortably dived using a dry suit.