Remains of an ice cave frozen into the Icelandic glacier lagoon

At dusk the waxing moon peeks through a tall iceberg arch with stripes of black volcanic ash on the frozen glacier lagoon Jökulsárlón on Iceland.
The northernmost parts of Iceland meet the Arctic Circle at 66° latitude, where armadas of icebergs drift south in the Arctic Ocean of the East Greenland Current. This ocean current almost reaches the northwestern coast of Iceland. The inland ice caps of Iceland receive annual snowfall of up to 15 m (50 ft). Despite these harsh Arctic conditions, Iceland’s coastal climate is surprisingly mild and temperate throughout the year. This is because Iceland’s climate in the midst of the North Atlantic is strongly influenced by the warm water current of the Gulf Stream. In addition, a warm recirculation branch of the Gulf Stream, the Irminger Current, encircles Iceland counterclockwise, preventing the coastal seawaters from freezing.
However, the regions in the vicinity of the large ice caps of Iceland produce their own regional climate, which may well be Arctic. It is mainly caused by cold winds, which flow from the ice caps into the valleys and out onto the sea. These gravity-driven catabatic winds can reach gale force and drastically reduce temperatures compared to the adjacent regions. This is the main reason why the brackish water of the lagoon of the glacial lake of Jökulsárlón can completely freeze up in winter, allowing direct access to the icebergs. The frequency and intensity of these catabatic winds again depends on the large-scale meteorological conditions. Thus, around the Vatnajökull ice cap, a regional and capricious climate system is formed that fluctuates between arctic and temperate conditions.
This impressive ice arch of 7 m height (23 ft) is the remains of an ice cave from which the Breiðamerkurjökull glacier once discharged its meltwater stream into the ice lake. The ice is about 1000 years old and contains two ash layers from the volcanic eruptions of Grímsvötn. This volcano is one of the most active in Iceland and hides completely under the Vatnajökull ice cap. Its collapsed crater, called caldera, contains a lake that never freezes under the ice. Grímsvötn’s eruptions are always highly explosive because the lava comes into contact with the meltwater. If this happens, catastrophic meltwater floods occur, the Jökulhlaups. These flash floods destroy everything in their path until they reach the Atlantic Ocean. The lava, on the other hand, spreads as finest ash over wide areas and is preserved in the glacier over long periods of time. With the thaw in spring this gate to the Arctic was carried out by the tides into the ocean, where it disappeared forever in the surf of the North Atlantic.