Silfra and Plate Tectonics

Tectonic plates are the pieces of the Earth’s crust, together with the uppermost part of the Earth’s mantle, that create the lithosphere. These pieces are not stagnant, and interact with each other in different ways: convergence, divergence, and transform.

Convergence occurs when two plates slide towards each other. The denser plate moves underneath the less dense plate to create the subduction zone. The magma from the mantle creates either continental volcanoes or volcanic islands, depending on if the convergence is with continental plates against each other or oceanic plates. Trenches are also formed, and earthquakes occur across the affected areas.

Divergence is when two plates spread apart. In the ocean, this is caused by seafloor spreading. Small volcanoes and shallow earthquakes are often a result of divergence.

Tectonic plates transform if they slide next to, or grind against, each other, causing faults. Earthquakes occur along fault lines.

Silfra is the result of divergence. When the North American and Eurasian Tectonic plates moved apart, lava was pushed out from underneath the crust, eventually forming the Mid-Atlantic Ridge. The divergence is not finished, as the area continues to move apart 2 cm every year. This puts an incredible amount of tension on the surrounding area, resulting in massive earthquakes approximately every ten years.

Silfra is a tectonic fissure in Thingvellir. When it formed, an underwater spring was broken and thus Silfra was filled with incredibly clear water, allowing for the greatest underwater visibility accessible for diving.

Despite Silfra being a diving hot-spot, there are very distinct parts of the fissure that are permitted for such activities. The cave system within the fissure, though fascinating, is dangerous, and the massive earthquakes also pose a threat for safety.