Blue ice like this deep blue occurs over hundreds of years and begins when simple snow falls onto ice or in this case a glacier. The snow sticks to the ice and has its air bubbles forced out during the movement of the glacier or transit of the ice. Then this snow freezes more to become ice crystals and becomes clearer.
Located at the bottom of the 6,921 feet tall Vrffajvkull, Iceland's tallest active volcano, the Crystal Cave of Svmnafellsjvkull is accessible through a 22-foot entrance on the shoreline. However because of the instability of ice cave, it is advisable to visit in winter when the cold temperatures harden the ice.