The earth's crust, the solid upper mantle of earth's inner structure is broken up into tectonic plates which move separately from each other. Moving along on the oceanic crust made of basaltic rocks, the continental crusts largely made from granitic rocks float around, converge, diverge, causing seismic events and volcanic activity.
In Iceland the Mid-Atlantic ridge becomes visible as a fault where the North American and Eurasian tectonic plates meet.
The fault visible on this location, filled with water, an underwaterworld visited by divers for the clearwaters and all out experience.
Upper-picture, North American plate, lower picture, Eurasian plate.
Iceland's medieval parliament, the world's first, used to meet in Thingvellir valley, also a place where the two plates cause a dramatic landscape.