Cryostratigraphy of Rhythmic Segregated Ice in Colluvium and Implications for Permafrost Slope Stability

ABSTRACT The amount and stratigraphic setting of ground ice in permafrost slopes is a key control on the style and magnitude of permafrost mass wasting. Understanding the spatial and stratigraphic variations in ground ice distribution on permafrost slopes is therefore a fundamental property in assessing the stability of permafrost hillslopes. Most recent investigations into mass wasting of permafrost slopes have focused on characterizing differences between ground ice types in cold, continuous permafrost regions to infer ice genesis, which primarily involves contrasting relict glacier ice to intrasedimental ice. However, ground ice assemblages in warmer, discontinuous permafrost slopes are poorly understood and have experienced widespread thawing of relict ice coupled with post‐thawing permafrost aggradation and ground ice development on slopes. Here, we present a detailed description of ground ice bodies from a mining cut and thaw slump exposure in the Klondike Region of Yukon, Canada, to infer the setting and genesis of the massive ice preserved in slope materials of warm, discontinuous permafrost. Ground ice bodies are characterized using a cryostratigraphic approach combined with computed tomography scanning and stable O–H isotopic and dissolved ion analyses. A unique suite of ground ice consisting of ice layers up to 1 m thick, rhythmically alternating with ice‐rich colluvium with conformable upper contacts is identified. This milky‐white ice is largely clear of sediment inclusions with moderate ion concentrations and numerous tubular bubble trains oriented parallel to slope. The δ 18 O values of the ice indicate that the source of water consists of summer and winter precipitation, and the δ 18 O–δD regression slope suggests that the ice was formed in an open system with the addition of meteoric water. These results are distinct from other ground ice types at the site, and collectively indicate that these rhythmic ice layers are a product of segregated ice layer growth interspersed with episodes of thaw‐driven mass wasting on an aggrading permafrost hillslope. Finally, the significance of repeated segregated ice growth on permafrost slope stability is discussed drawing on an example of recent permafrost mass wasting in the central Mackenzie Valley, Northwest Territories, Canada.