— The crystal cave
THIS FROZEN PALACE is a cave running beneath Iceland’s Vatnajökull, or Vatna Glacier. At 3,100 cubic kilometres, Vatnajökull is the largest European ice cap by volume and averages 400 metres thick.
This means its ice is so densely packed that any air bubbles are squeezed out, giving the ice a crystal clarity and its blue hue. Air bubbles normally scatter sunlight, giving ice a white sheen; without them, water molecules absorb red, orange, yellow and green light and reflect only blue and violet.
The ground beneath Vatnajökull runs red hot, with volcanic vents bubbling hot springs to the surface. Running water from ice melting beneath the glacier or meltwater from the surface sculpts the cave’s scalloped ceiling – the same phenomenon is also seen in limestone caves carved out by streams.