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Abstract Iceberg calving strongly controls glacier mass loss, but the fracture processes leading to iceberg formation are poorly understood due to the stochastic nature of calving. The size distributions of icebergs produced during the calving process can yield information on the processes driving calving and also affect the timing, magnitude, and spatial distribution of ocean fresh water fluxes near glaciers and ice sheets. In this study, we apply fragmentation theory to describe key calving behaviours, based on observational and modelling data from Greenland and Antarctica. In both regions, iceberg calving is dominated by elastic-brittle fracture processes, where distributions contain both exponential and power law components describing large-scale uncorrelated fracture and correlated branching fracture, respectively. Other size distributions can also be observed. For Antarctic icebergs, distributions change from elastic-brittle type during ‘stable’ calving to one dominated by grinding or crushing during ice shelf disintegration events. In Greenland, we find that iceberg fragment size distributions evolve from an initial elastic-brittle type distribution near the calving front, into a steeper grinding/crushing-type power law along-fjord. These results provide an entirely new framework for understanding controls on iceberg calving and how calving may react to climate forcing. 

Abstract. Crevasses are affected by and affect both the stresses and the surfacemass balance of glaciers. These effects are brought on through potentiallyimportant controls on meltwater routing, glacier viscosity, and icebergcalving, yet there are few direct observations of crevasse sizes andlocations to inform our understanding of these interactions. Here we extractdepth estimates for the visible portion of crevasses from high-resolutionsurface elevation observations for 52 644 crevasses from 19 Greenlandglaciers. We then compare our observed depths with those calculated usingtwo popular models that assume crevasse depths are functions of localstresses: the Nye and linear elastic fracture mechanics (LEFM) formulations.When informed by the observed crevasse depths, the LEFM formulation produceskilometer-scale variations in crevasse depth, in decent agreement withobservations. However, neither formulation accurately captures smaller-scalevariations in the observed crevasse depths. Critically, we find thatalong-flow patterns in crevasse depths are unrelated to along-flow patternsin strain rates (and therefore stresses). Cumulative strain rate ismoderately more predictive of crevasse depths at the majority of glaciers.Our reliance on lidar limits the inference we can make regarding fracture depths. However, given the discordant patterns in observed and modeled crevasses, we recommend additional in situ and remote sensing analyses before Nye and LEFM models are considered predictive. Such analyses should span extensional and compressive regions to better understand the influence of advection on crevasse geometry. Ultimately, such additional study will enable more reliable projection of terminus position change and supraglacial meltwater routing that relies on accurate modeling of crevasse occurrence.