Silfra is a rift valley that runs along part of the Mid-Atlantic Ridge in Iceland. This picture of Silfra shows an area where large cracks formed as the North American Plate and the Eurasian Plate moved away from each other. In this area, the rift cuts through an underwater spring, causing the cracks to fill with crystal-clear water. Because the water is so clear, it is a popular spot for scuba divers.