Laboratory frost sorting by needle ice: a pilot experiment on the effects of stone size and extent of surface stone cover

Abstract

Sorted patterned ground is ubiquitous where gravelly fine soil experiences freeze–thaw cycles, but experimental studies have rarely been successful in reproducing such patterns. This article reports an attempt to reproduce miniature sorted patterns by repeating needle‐ice formation, which simulates frost sorting in regions dominated by diurnal freeze–thaw cycles. Six full‐scale laboratory models were tested. They consisted of near‐saturated volcanic fine soil topped by small stones of uniform size; the models explored a range of stone size (~6, ~12, ~17 and ~22 mm) and surface abundance (20, 40 and 60% cover). The stones were placed in a grid on the surface. These models were subjected to 20–30 temperature excursions between 10 °C and −5 °C in 12 hours. The evolution of surface patterns were visually traced by photogrammetry. A data logging system continuously monitored vertical soil displacements, soil temperatures and moistures at different depths. All experimental runs displayed needle‐ice formation (2–3 cm in height) and resulting displacement of stones. The soil domains tended to heave faster and higher than the stones, leading to outward movement of the former and concentration of the stones. In plan view, smaller stones showed relatively fast and long‐lasting movements, while larger stones stabilized after the first five cycles. The 20% stone cover produced stone islands, whereas the 40% cover resulted in sorted labyrinths (a circle‐island complex) that may represent incipient sorted circles. The average diameter or spacing of these forms are 12–13 cm, being comparable to those in the field. The experiments imply that needle‐ice activity promotes rapid formation of sorted patterns, although the formation of well‐defined sorted circles may require hundreds of diurnal frost heave cycles. Copyright © 2014 John Wiley & Sons, Ltd.

Frost sorting on slopes by needle ice: A laboratory simulation on the effect of slope gradient

“…Lateral stone movements resulted in slight sorting within the first five cycles (Figure C), but rapid downslope movements obscured the sorting and, instead, resulted in downslope accumulation of almost all stones. The stone transport was still active after 40 cycles, but this model did not produce any clear surface geometry; following Yamagishi and Matsuoka (), we call this ‘unclear pattern’.…”

“…The situation may reflect a retrograde component due to the cohesion of soil (Matsuoka, ), but generally smaller heave on stones than on soil domains is more source for the overestimation (cf. Yamagishi and Matsuoka, ).…”

“…Yamagishi and Matsuoka () reported results from a pilot experiment exploring the effects of sizes and abundance of surface stones on the geometry of surface patterns on flat ground subjected to short‐term freeze–thaw cycles. We follow this approach to simulate needle ice‐induced frost sorting on slopes that may produce stripe patterns.…”

“…This situation can be improved by laboratory experiments that accelerate the process, explore the effects of contributing factors, and may finally reproduce miniature sorted patterned ground. Yamagishi and Matsuoka (2015) reported results from a pilot experiment exploring the effects of sizes and abundance of surface stones on the geometry of surface patterns on flat ground subjected to short-term freeze-thaw cycles. We follow this approach to simulate needle ice-induced frost sorting on slopes that may produce stripe patterns.…”

“…As a first step we address the effects of slope gradient. To complement the methods used in Yamagishi and Matsuoka (2015), we use new software to track the three-dimensional trajectories of marked stones.…”