Prospects for observations of high-energy cosmic tau neutrinos

We study the prospects for the observation of high-energy cosmic tau neutrinos $(Eg~{10}^{6}$ GeV) originating from proton acceleration in the cores of active galactic nuclei. We consider the possibility that vacuum flavor neutrino oscillations induce a tau to muon neutrino flux ratio greatly exceeding the rather small value expected from intrinsic production. The criteria and event rates for under water or ice light \ifmmode \check{C}\else \v{C}\fi{}erenkov neutrino telescopes are given by considering the possible detection of downgoing high-energy cosmic tau neutrinos through characteristic double shower events.