This is my postdoc work with Deborah Sulsky and Buck Schreyer. We used a decohesive constitutive model, developed mainly by Buck & Deborah, implemented in an MPM code to study the formation of leads in the Arctic ice sheet. The scale of the problem (hundreds of kilometres) can be seen in the movie. I got a lot of inspirations from Deborah & Buck on how an engineering problem must be solved by a mathematical tool. It's a good lesson for me, an engineer, from a mathematician (Deborah). My thinking about and also obsessions with large scale issues together with the MPM rooted from this period. This led later to the development of a multi-scale constitutive modelling framework. The below movie was a result of my postdoc work. The ice sheet (left part is an island) moves under wind and ocean condition together with the Coriolis force. This non-proportional loading induces fracturing and also ridging when the loading path changes. My motivation on how energy is dissipated and how to capture that in constitutive modelling came from this. In the movie, the determinant of the deformation gradient F is plotted over time to indicate the formation of leads (fracture) or ridges (compaction).