  We report elastic and inelastic neutron scattering experiments on different
amorphous ice modifications. It is shown that an amorphous structure (HDA')
indiscernible from the high-density phase (HDA), obtained by compression of
crystalline ice, can be formed from the very high-density phase (vHDA) as an
intermediate stage of the transition of vHDA into its low-density modification
(LDA'). Both, HDA and HDA' exhibit comparable small angle scattering signals
characterizing them as structures heterogeneous on a length scale of a few
nano-meters. The homogeneous structures are the initial and final transition
stages vHDA and LDA', respectively. Despite, their apparent structural identity
on a local scale HDA and HDA' differ in their transition kinetics explored by
in situ experiments. The activation energy of the vHDA-to-LDA' transition is at
least 20 kJ/mol higher than the activation energy of the HDA-to-LDA transition.
