Periglacial puzzles: Unravelling environmental controls on alpine solifluction lobe dimensions and shape

Freeze-thaw processes cause periglacial creep (solifluction) which forms solifluction lobes: lobate features characterized by a steep riser (front) and a smooth tread (body). Despite the widespread occurrence of these lobes, the controls on their morphometry remain poorly understood. Research into solifluction lobe morphometry is crucial for understanding their role in landscape evolution, hydrology, sediment budgets, and providing microhabitats in a warming climate. We mapped geomorphic and vegetation properties of 40 solifluction lobes in the Turtmann Valley, Swiss Alps, and recorded soil moisture and temperature with a TOMST TMS4 logger at a 10-minute interval for nearly two years. We combined these data with derivatives of a high-resolution digital elevation model and conducted a Spearman ranked correlation test. Our results revealed that: (i) The largest lobes, with the highest risers occur in areas with high flow accumulation (𝝆 = 0.40-0.75). (ii) Wider, lobate lobes dominate at higher elevations (𝝆 = 0.49) on north-exposed slopes (𝝆 = 0.53) with long snow (𝝆 = 0.47-0.58) and sparse vegetation cover, while narrow, tongue-shaped lobes occur at lower elevations with high vegetation cover (𝝆 = 0.38-0.55), suggesting a strong topoclimatic control. (iii) Lobes in the Turtmann Valley are longer and more tongue-shaped, with higher risers and on steeper slopes, than many lobes previously studied. Overall, our results suggest that alpine solifluction lobe dimensions and shape are controlled by different set of environmental factors than arctic lobes, possibly due to effects of stronger topoclimatic gradients, steeper slopes and higher flow accumulation on mountain slopes.