Solifluction and mudflow on a limestone periglacial slope in the Swiss Alps: 14 years of monitoring

The dynamics of stone‐banked lobes were investigated by monitoring soil movements and environmental parameters over 14 years on a limestone slope subject to deep seasonal frost. The monitored parameters included downslope soil movement, frost heave, soil temperature, moisture and snow depth. Despite being composed of the same soil, lobes on the upper slope (∼20°) display pressure ridges on the tread and terminate in a high riser (∼1 m), whereas lobes on the lower slope (∼10°) have a flat tread and a low riser (∼0.5 m). The long‐term monitoring demonstrates that gelifluction, resulting from seasonal frost heave of approximately 5 cm and thaw settlement, occurs annually in the lower lobes at a mean surface rate of 4 cm a−1 and with a movement base at approximately 40‐cm depth. The rate of gelifluction shows some interannual fluctuation depending primarily on the annual frost heave amount, but overall regularity of the rate and depth of movement regardless of seasonal frost depth results in lobes having similar morphologies. On the upper, steeper lobes located just below late‐lying snow patches, rapid, shallow mudflows (∼20 cm thick) are often superimposed on gelifluction. The rate of surface movement varies spatially, in places exceeding 2 m per event. The prolonged water supply and low consistency limits of the limestone soil favour mudflows on seasonal thawing. The transported sediments pile up near the lobe front, resulting in a high riser. Such modification of solifluction lobes by mudflows can occur in other slopes with similar gradients, soils, frost and snow conditions. Copyright © 2010 John Wiley & Sons, Ltd.