Large dune fields occupy more than 500,000 km2 of the East Antarctic Plateau. The megadunes, or long-wavelength surface ripples, have amplitudes of only a few meters, wavelengths of a few kilometers, and parallel crests which can extend one hundred kilometers. They occur in areas characterized by low accumulation, extensively recrystallized snow, and strong scattering of the microwave part of the spectrum. Dune crests are oriented perpendicular to the regional katabatic wind direction. Snow megadunes are unlikely to be formed by simple wind transport of snow particles. ¿ 2000 American Geophysical Union