Stone size and velocity transported by needle ice activity

Abstract

Downslope movements of 12 stones (10–27 cm in diameter) were determined from time-series images over 21 years on a Japanese alpine debris slope. Frost heave occurred 24–85 times/a with an annual maximum amount of 1.8–5.6 cm. Stones moved downslope at 4–16 cm/a, the velocity correlating with the stone size. Extrapolation suggests that needle ice can transport stones with a diameter of 30 cm or more. Both annual mean air/soil temperatures and frost heave activity slightly increased during 21 years. Climatic warming may have raised the frequency of needle ice by shortening the snow-covered period.