An instrument designed to determined the three-dimensional velocity and mass distribution of ions with energy per charge up to 3 eV was flown for the first time as part the Lagopedo Uno rocket experiment, the purpose of which was to deplete artificially the ion concentration in the F layer ionosphere over Hawaii. The device measured relative ion densities and directionality; mass analysis between 1--32 amu/e was performed by using a time-of-flight technique. The depletion was achieved by detonating an explosive charge which released 1027 molecules of H2O, accompanied by lesser amounts of NO and CO2. At the time of the explosion the densities of all ion species were At the time of the explosion the densities of all ion species were reduced below the limit of detectability for 2.5 s. Over the next 60 s, as the instrument package moved 30 km away from the detonation + was again detected but at a concentration only half that expected from prevent levels and altitude corrections. The O+2 concentration within 60 s and 30 km of the explosion was up to 3 times its earlier value. During the same space and time intervals the O+ mean velocity had a component of velocity perpendicular to the line joining the detector and the detonation location, consistent with an electric field, ~10 mV/m, pointing toward the center of the 'hole'. Later, while the instrument package was 30 km from th exposion site, the O2+ density was seen to increase again, while the O+ density remained below the unperturbed value. The contaminants therefore reached 30 km within 2 min. The behavior of O+ compares favorably with predictions from a simple spherical diffusion model of H'd2O.H2O+ could not be observed, since it overlapped the O+ mass channel and was expected to be much less than the latter. H+ did not respond to the event except for the dropout of 2.5 s. These measurements of ion composition and depleted region growth pattern are in general agreement with theoretical descriptions of such events, such as that of Bernhardt (1976).