  We describe the phase diagram of amorphous solid water by performing
molecular dynamics simulations. Our simulations follow different paths in the
phase diagram: isothermal compression/decompression, isochoric cooling/heating
and isobaric cooling/heating. We are able to identify low-density amorphous
(LDA), high-density amorphous (HDA), and very-high density amorphous (VHDA)
ices. The density $\rho$ of these glasses at different pressure $P$ and
temperature $T$ agree well with experimental values. We also study the radial
distribution functions of glassy water. We obtain VHDA by isobaric heating of
HDA, as in experiment. We also find that ``other forms'' of glassy water can be
obtained upon isobaric heating of LDA, as well as amorphous ices formed during
the transformation of LDA to HDA. We argue that these other forms of amorphous
ices, as well as VHDA, are not altogether new glasses but rather are the result
of aging induced by heating. Samples of HDA and VHDA with different densities
are recovered at normal $P$, showing that there is a continuum of glasses.
Furthermore, the two ranges of densities of recovered HDA and recovered VHDA
overlap at ambient $P$. Our simulations are consistent with the possibility of
HDA$\to$LDA and VHDA$\to$LDA transformations, reproducing the experimental
findings. We do not observe a VHDA$\to$HDA transformation.
