CGCircuit - Applied Houdini - Particles V
https://www.cgcircuit.com/course/applied-houdini---particles-v

Particles V - Grains is here to teach you how to make epic snow/sand/mud effects with grains in the Vellum Solver, also known as PBD (point based dynamics)! In this lesson we will quickly learn how to efficiently simulate millions of tiny stacking particles in order to make a snowy expanse collapse into a sinkhole. Along the way we'll control various properties and constraints to control our grain simulation, as well as cover novel geometry and rendering based tricks to make our snow look as good as possible. Start playing with snow with grains today!