Published online 1 September 1999 | Nature | doi:10.1038/news990902-9


Natural snowballs

Writing in the August issue of the Journal of Glaciology, T. Kameda of the Kitami Institute of Technology, Kitami, Hokkaido, Japan and colleagues describe the formation of natural snowballs at Dome Fuji station in Antarctica. However, before small children clamour to be sent there, a few details of the conditions under which they form may perhaps deter them. These balls of snow form best deep in the Antarctic winter, when the air temperature is below minus 60 °C (minus 76 °F), and there is a gentle wind blowing - conditions under which even well-equipped polar explorers stay in heated buildings. In this frigid environment, delicate needles of hoar frost form on the surface of the snow. Some of these are rolled about by the wind and create these fragile snowballs, which grow to a size of about 30 mm.

The balls develop on the surface of the ice in less than 24 hours - understandably, Kameda's team only examined the ground once a day under such rigorous conditions. Once the snowballs have formed, the wind trundles them along the ground until they collect in small wind-carved hollows in the snow.

The extreme climate in which they form is the most likely reason why they have not been reported in detail before now. Only two reports from earlier observers may describe the same phenomenon. Roald Amundsen reported cylinders of snow on his journey towards the Pole in 1911, and Paul Siple at the South Pole in 1957 recorded observations of wispy balls of frost up to 50 mm across. However, in neither case is it clear that this is the same thing, so Kameda and colleagues are the first clear discoverers of this intriguing natural formation.

The researchers gave these dainty formations the name 'yukimarimo'. 'Yuki' is the Japanese for snow, and 'marimo' is a globular water plant found in a lake in Hokkaido, Japan's northern island. Marimo are highly esteemed in Japan, being designated a Special Japanese Natural Treasure for their beauty. The researchers saw a likeness between these velvety green spherical plants and this novel frost formation. The resemblance is, perhaps, one that only a home-sick worker in the monochrome world of the polar regions would see.