## 6 Conclusions  
This paper quantified high spatial-temporal ice flow speeds, sea ice backscatter and melt-water ponds with multi-source remote sensing datasets and calculated the stress and damage of a floating ice tongue using a numerical ice flow model, to understand the precursors and causes for a calving event that occurred in July 2017 at the Petermann Glacier, northern Greenland. The weakening of landfast sea ice reduces the buttressing force for the glacier terminus as its extent declines, which most directly leads to calving. Additionally, tributary glacier extrusion and shear also play roles in destabilizing the frontal shear zone. In addition, multiple melt ponds evolve to fill in fractures, which may induce the hydrofracturing and weaken the floating ice structure as a precondition of triggering subsequent frontal collapse. In total, we infer that weakening sea ice, shearing due to inflow from the tributary glacier and meltwater in crevasses may all have led to this calving event. The joint use of dense remote sensing observations and numerical ice-flow models for a quick ice-flow system will deepen our understanding of the hydrological and kinematic precursors of frontal collapse in Greenland ice shelves and its response to climate change.  
The following are available online at [[https://www.mdpi.com/2072-4](https://www.mdpi.com/2072-4)]([https://www.mdpi.com/2072-4](https://www.mdpi.com/2072-4)) 292/13/4/591/s1, Table S1-S4: satellite images list. Table S1: Ice Velocity retrieved from Sentinel-2 satellite images; Table S2: Melt Pond calculation of Sentinel2 images from Google Earth Engine; Table S3: Sea Ice Extent retrieved from Landsat-8 satellite images; Table S4: Backscatter retrieved from Sentinel images from Google Earth Engine.  
The idea of this research was conceived by [PERSON] and [PERSON]; methodology, [PERSON], [PERSON], and R.H.; experimental data was processed and analyzed by [PERSON]; writing--original draft, [PERSON] and [PERSON]; writing--review and editing, [PERSON] All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key R&D Program of China (grant number 2018 YFC1406102 and 2017 YFA0603103), the Strategic Priority Research Program of the Chinese Academy of Sciences (grant number XDA19070104) and the Key Research Program of Frontier Sciences, CAS (grant number QYZDB-SSW-DQC027 and QYZDJ-SSW-DQC042).  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
All the results and data generated during the study, i.e., ice velocity, stress, etc., can be accessed by request from the first author ([EMAIL_ADDRESS]).  
The authors would like to thank the ESA for providing free Sentinel-2 images ([[https://scihub.copernicus.eu/dhus](https://scihub.copernicus.eu/dhus)]([https://scihub.copernicus.eu/dhus](https://scihub.copernicus.eu/dhus))), Landsat 8, the Google Earth Engine Platform and the ISSM model in JPL offered; and thanks goes to [PERSON] for providing the COSI-Corr software package. We also thank the two anonymous reviewers for providing feedback and suggestions that significantly improved the paper.  
The authors declare no conflict of interest.