Whumping On Depth Hoar

My group was just spending afternoon to dig several snow profile pits to find out December Depth Hoar between 85-120 cm down from the surface. Hight of snow at this place was between 120-140cm and compression test result was moderate sudden collapse average 100cm down. We did an extended column test (ECT) and its result was ECTP 28 down 100cm after we heard a whumping. Then, rain began to come down late this afternoon below 1800m.