Scientists have discovered a rift the size of the Grand Canyon hidden under the Antarctic ice sheet, which they say is contributing to ice melt and a consequent rise in the sea level.

The rift, some 1.5 kilometres deep, 10 kilometres wide and 100 kilometres long, was found by researchers using radar to measure the subglacial topography. 

Glaciologist Robert Bingham said scientist believe a shrinking West Antarctic Ice Sheet is responsible for about 10 per cent of climate-change-induced sea level rise, which if unchecked threatens to flood many coastal cities within a few generations. 

The sheet, a huge mass of ice up to four kilometres thick that covers the land surface and stretches into the sea, is melting faster than any other part of Antarctica.