— The crys­tal cave

Cosmos - - Contents -

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.

IM­AGE Stan­son / Getty Im­ages

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