Waves wash ashore on the black sandy beach of Vik in Iceland

The full moon rises over the coastline of Vik Strandur and the rock spires of Reynisdrangar on Iceland. At dusk, shortly before midnight in midsummer, the waves roll endlessly up against the black lava beach and paint magnificent structures along the shore line.
The fine-grained black beaches of southern Iceland consist of volcanic sand from eroded basalt cliffs and dykes like the Reynisdrangar rock spires. In addition, vast amounts of black sand originate from Jökulhlaup events. These deluge-like floods occur when volcanoes erupt under the ice caps and abruptly melt the ice. These uncontrollable meltwater flash floods carry fine grained ashes, coarse sands and bouldery rocks out into the ocean.
The sandy volcanic sediment is transported along the coastline in a zigzag pattern because the incoming waves and the outgoing backwash differ in angle. Waves travel at oblique angles to the beach, which depend on the local wind, while the backwash is always perpendicular to the beach because it is purely gravity-driven. The resulting lateral transport of the sediment is superimposed by currents and tides. The full moon over Vik Strandur indicates high tide.
The North Atlantic around Iceland is strongly influenced by the warm Irminger Current, which is a recirculation branch of the warm Gulf Stream. This explains why the water temperatures along the coasts of Iceland are above the freezing point of -1.8°C (28.8° F) throughout the year.
The volcanic foundation of Iceland does not end at its beaches. The rock platform extends a further 90 km (56 mi) into the sea, where the average water depth is just -300 to -400 m (-1000 to -1300 ft). Beyond that, however, the seabed drops gently to depths of -2000 to -3000 m (-6000 to -9000 ft).
It is a very special emotion to experience the twilight shortly before midnight. The night in the south of Iceland lasts only one hour in midsummer.