On the 98% ice covered Antarctic continent there are only few places that are permanently clear of ice. The "McMurdo Dry Valleys", which are visible on this photo, are the largest ice-free area on the continent, and receive only about one centimetre of annual snowfall. Because the snowfall rate is much smaller than the evaporation rate, the snow vanishes almost immediately after falling. This is due to the cold and dry catabatic wind that is almost permanently descending from the interior of the dome-shaped continent down to the coasts - sometimes with more than 250 km/h !