Angle of Repose for Graupel

January 28, 2021



Photographer: Roger Hopkins
Summary Author: Roger Hopkins

The Nor’easter that visited the northeast U.S. on December 16-17, 2020, brought 13 inches (33 cm) of fine-grained graupel to Lansing, New York, and an amazing 40 plus inches (100 cm) of snow and graupel to Binghamton, about 40-miles (64 km) to the southeast. The above photos show the angle of repose of these small uniform graupel pellets as they accumulated on horizontal surfaces. Graupel pellets bounce on impact and roll like tiny BBs off the edges of the pile. After a few hours, the pellets within the pile can weld together and as the height of the pile increases, fewer will land on the top, creating a pointed witches hat shape. My measurements show an angle of approximately 65 degrees. Note that the Avalanche Handbook and other sources show values that range from 35 degrees to as high as 80 degrees.  

The top photo (at left, courtesy of Scott Geiger of Binghamton) shows his car with piled-up graupel that was still growing when the storm abated, while the fence posts (at top right in Lansing) could only sustain 3 inches (8 cm) high caps. The bottom photo illustrates the interesting effect on a round rotating surface; two soda bottles forming my squirrel barrier that will henceforth be called my snow accumulation rotisserie.