Search for: All records

Abstract Rock glaciers dominate the cryosphere in mid‐latitude alpine settings, yet their activity and their histories remain challenging to constrain. We focus on the Thomas Lake rock glacier on Mt. Sopris in Colorado, USA. We measure surface velocities by feature tracking of image pairs and document Holocene¹⁰Be exposure ages on surface debris. The surface speeds average 0.8 m/yr and peak at 2 m/yr in a steep reach. Exposure ages range from 1.4 to 13.2 kyr and monotonically increase down‐glaciers. Ages exceeding 6 kyr occur in the bottom quarter of the landform, coinciding with sporadic tree cover. These constraints constrain a numerical model of Holocene rock glacier activity. In our model, surface velocity is entirely explained by the deformation of the ice‐rich core with the extra load of the rocky carapace. Surface mass balance is simplified to an accumulation area of ice and debris equivalent to the avalanche cone, and very low, uniform ablation in the remaining rock glacier where rock cover minimizes melt. Climate drives the activity through a history of ice accumulation in the avalanche cone. Matching the observed age and speed structure requires: (a) Early Holocene growth of the rock glacier, (b) low accumulation during the middle Holocene warm period (Hypsithermal), and (c) two Neoglacial accumulation pulses, the most recent being the Little Ice Age. Pulses travel down the valley as kinematic waves, re‐activating the landform. The headwall retreat rate of 4 mm/yr, inferred from rocky layer thickness and surface speed, far outpaces bedrock down wearing rates. 

Basal channels, which are troughs carved into the undersides of ice shelves by buoyant plumes of water, are modulators of ice-shelf basal melt and structural stability. In this study, we track the evolution of 12 large basal channels beneath ice shelves of the Amundsen and Bellingshausen seas region in West Antarctica using the Landsat record since its start in the 1970s through 2020. We observe examples of channel growth, interactions with ice-shelf features, and systematic changes in sinuosity that give insight into the life cycles of basal channels. We use the last two decades of the record, combined with contemporary ice-flow velocity datasets, to separate channel-path evolution into components related to advection by ice flow and those controlled by other forcings, such as ocean melt or surface accumulation. Our results show that ice-flow-independent lateral channel migration is overwhelmingly to the left when viewed down-flow, suggesting that it is dominated by Coriolis-influenced ocean melt. By applying a model of channel-path evolution dominantly controlled by ice flow and ocean melt, we show that the majority of channels surveyed exhibit non-steady behavior that serves as a novel proxy for increased ocean forcing in West Antarctica starting at least in the early 1970s. 

Abstract. In late March 2011, landfast sea ice (hereafter, “fast ice”) formed in the northern Larsen B embayment and persisted continuously as multi-year fast ice until January 2022. In the 11 years of fast-ice presence, the northern Larsen B glaciers slowed significantly, thickened in their lower reaches, and developed extensive mélange areas, leading to the formation of ice tongues that extended up to 16 km from the 2011 ice fronts. In situ measurements of ice speed on adjacent ice shelf areas spanning 2011 to 2017 show that the fast ice provided significant resistive stress to ice flow. Fast-ice breakout began in late January 2022 and was closely followed by retreat and breakup of both the fast-ice mélange and the glacier ice tongues. We investigate the probable triggers for the loss of fast ice and document the initial upstream glacier responses. The fast-ice breakup is linked to the arrival of a strong ocean swell event (>1.5 m amplitude; wave period waves >5 s) originating from the northeast. Wave propagation to the ice front was facilitated by a 12-year low in sea ice concentration in the northwestern Weddell Sea, creating a near-ice-free corridor to the open ocean. Remote sensing data in the months following the fast-ice breakout reveals an initial ice flow speed increase (>2-fold), elevation loss (9 to 11 m), and rapid calving of floating and grounded ice for the three main embayment glaciers Crane (11 km), Hektoria (25 km), and Green (18 km).