Oxygen vacancies in SiO2 have long been regarded as bistable, forming a Si-Si dimer when neutral and a puckered configuration when positively charged. We report first-principles calculations of O vacancies in amorphous SiO2 supercells that unveil significantly more complex behavior. We find that the vast majority of O vacancies do not pucker after capture of a hole, but are shallow traps. The remaining vacancies exhibit two distinct types of puckering. Upon capturing an electron, one type forms a metastable dipole, while the other collapses to a dimer. A statistical distribution of O vacancies is obtained, and the implications for charge transport and trapping in SiO2 are discussed.