The sudden propagation of a major preexisting rift (full-thickness crack) in late 2016 on the Larsen C Ice Shelf, Antarctica led to the calving of tabular iceberg A68 in July 2017, one of the largest icebergs on record, posing a threat for the stability of the remaining ice shelf. As with other ice shelves, the physical processes that led to the activation of the A68 rift and controlled its propagation have not been elucidated. Here, we model the response of the ice shelf stress balance to ice shelf thinning and thinning of the ice mélange encased in and around preexisting rifts. We find that ice shelf thinning does not reactivate the rifts, but heals them. In contrast, thinning of the mélange controls the opening rate of the rift, with an above-linear dependence on thinning. The simulations indicate that thinning of the ice mélange by 10 to 20 m is sufficient to reactivate the rifts and trigger a major calving event, thereby establishing a link between climate forcing and ice shelf retreat that has not been included in ice sheet models. Rift activation could initiate ice shelf retreat decades prior to hydrofracture caused by water ponding at the ice shelf surface.

2016 年底，南极洲拉森 C 冰架上的一个重大裂谷（全层裂缝）突然扩展，导致板状冰山 A68 于 2017 年 7 月崩解，这是有记录以来最大的冰山之一，对南极洲构成威胁。剩余冰架的稳定性。与其他冰架一样，导致 A68 裂谷激活并控制其传播的物理过程尚未阐明。在这里，我们模拟了冰架应力平衡对冰架变薄和包裹在预先存在的裂谷中和周围的冰混合物变薄的响应。我们发现冰架变薄不会重新激活裂缝，而是治愈它们。相比之下，混杂物的变薄控制裂谷的开口率，对变薄具有线性依赖性。模拟表明，冰混合体变薄 10 到 20 m 足以重新激活裂谷并引发主要的崩解事件，从而在冰盖模型中未包括的气候强迫和冰架退缩之间建立联系。裂谷激活可能在冰架表面积水引起水力破裂之前几十年开始冰架后退。