Study of high energy cosmic ray interactions at Chacaltaya Laboratory

Cosmic rays physics is currently studied with rather sophisticated detector s operating in a variety of either experimental conditions or atmospheric d epths in the world. In this paper we present the main properties of the obs erved features of high-energy nuclear interaction phenomena of cosmic rays, with particular emphasis on some experimental observations made by the emu lsion chamber technique at Chacaltaya Laboratory (Bolivia, 5230 m a.s.l.). A discussion on the past and present achievements as well as the future pro spects of high altitude mountain laboratories for cosmic ray physics is pre sented.