The relief of the rift alters at a geologically frenetic speed. Terrestrial forces separate the tectonic plates at a rate of 2.5 cm per year. This creates accumulated tension, which is released, approximately every 10 years, through an earthquake. Every time this happens, new caves, crannies and passageways are created.
This geological frontier, accessible only underwater, is reached via the second biggest lake in Iceland, the Þingvallavatn, in Þingvellir National Park, 60 km from Reykjavik. This park is the only place in the country that has been declared a UNESCO World Heritage Site; a cultural one, since it is where the first Icelandic Parliament, the Alþingi, was founded, in 930, considered the first parliament in the world. That is where Icelanders used to go to discuss laws and judge anyone who broke them. Men condemned to death were decapitated at a nearby waterfall, while women judged to be immoral or witches were drowned in the nearby lakes, known at that time as the ‘drowning pools’.
Nowadays, scuba divers go there to brave the 2 °C waters and, in dives that last 30–45 minutes
, they explore the nooks and crannies of an underwater labyrinth, comprising tunnels and caves, illuminated by the colours of external light reflected on the volcanic rocks. While the rift can reach as deep as 63 m, divers normally go down to about 18 m.