Holes containing cryoconite deposits visible in the bed of a melt water lake on the Petermann glacier. The surface of the glacier is covered with pot holes like these, which are often perfectly circular to the eye. The black granular cryoconite accelerates melting because the darker part of the spectrum lowers the albedo or reflectance of the usually white ice. A combination of these darker deposits, warmer melt water, the sun and the wind conspire to make these intriguingly geometric pot-holes in the ice. The sizes typically vary between 3cm and 30 cm in diameter and are between 3 and 500 cm deep.