Expansion of Solid Helium into Vacuum: the Geyser Effect
  The particle flux through a two micron diameter orifice into vacuum from a source chamber filled with solid He exhibits a striking periodic behavior similar to that of a geyser. This phenomenon is attributed to a periodic collapse of the solid inside the source induced by the accumulation of excess vacancies injected at the orifice. The flux-time curves agree well with a kinetic model and provide direct information on the diffusivity of vacancies in solid He. 
R. E. Grisenti, M. Kaesz, J. P. Toennies, G. Benedek, F. Dalfovo