While traveling today on the ridge between Main and Upper Days we had one very significant collapse (where it felt like we dropped at least an inch in elevation) and some active pit results nearby: We dug at (East, 9800,' 29 deg.) and had an ECTP21 down 55cm in one pit and an ECTV down 55cm in a pit only 5' away. These failures were on Fist 3-4mm facets on top of a pencil crust (degrading) in the old snow. HS 96cm.