Figure S6 : Photograph of GPS data collection site (67.048°N, -49.018 °W, elevation 1211.43 m). Measurements of ice surface motion were collected every 5 seconds using a Trimble R7 dual-frequency global positioning system (GPS) receiver and Trimble Zephyr GPS antenna affixed to a 3.3 m schedule-40 aluminum pole drilled vertically 3 m into the ice.