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INTRODUCTION
Interest in the brittle behaviour of ice shelves leading to fracture, iceberg calving and even disintegration, presents a challenging observational task because the tangible effects of fracture and calving are often difficult to discover until long after they occur. Fractures are hard to observe because they are often: (1) hidden from view (e.g., below surface snow, on the bottom of the ice shelf and/or below pixel size in imagery); (2) difficult to anticipate; and (3) difficult to address with sensors operating on periodic time schedules. Nevertheless, progress in understanding ice-shelf changes caused by brittle behaviour is needed, which motivates observational attention to brittle behaviour whenever and wherever it occurs. Ultimately, better understanding of ice-shelf brittle behaviour will allow assessment of the probability for imminent iceberg calving and ice-shelf break-up, such as that which occurred on the Larsen B Ice Shelf in 2002 (e.g., Glasser and Scambos, 2008; Banwell and others, 2013).
Examples of observational studies addressing ice-shelf brittle behaviour include the multi-year view of rifting on Pine Island Glacier and the Amundson Sea coast (MacGregor and others, 2012; Jeong and others, 2016), the study of rifting and calving on the Ross Ice Shelf leading to iceberg C19 (Joughin and MacAyeal, 2005) and study of the 'loose tooth' rift system on the Amery Ice Shelf (Bassis and others, 2008; Walker and others, 2013, 2015). Although extremely valuable, these previous studies exemplify that typically only one observational system (e.g., a satellite remote-sensing platform) is involved in recording the rifting/calving process, meaning that it has often been hard to pin down the exact timing and potential cause(s) of the events. In the present study, we report on a calving and rifting event of the McMurdo (McM) Ice Shelf (Fig. 1) that fortuitously (due to its location near the US National Science Foundation McM Station and the Antarctica New Zealand Scott Base) happened at a time and in an area where different types genres of observations, ranging from satellite imagery to ground survey, could be used to assess its causes. The goals of this study are to present this context and to seek the cause of the calving and rifting event so as to better inform similar...