"Glass is a supercooled liquid whose viscosity has become so high that for all practical purposes, it is a solid."
Glass experts know that a glass beam supported at the ends, with a weight hanging from the middle, will become measurably bent after many years due to slow viscous flow due to rearrangement of internal bonds.
Glass formation from thermonuclear melting of silicates is not at all an unexpected result. Compared to metals, molten silicates are very viscous and do not recrystallize very quickly.
Melting of high-purity (quartz) sand is an industry for making glass articles for high-temperature service. The names for this glass are "fused quartz" or "vitreous silica." Its desirability in manufactured articles is that it shows very high resistance to thermal shock breakage because of its very low thermal expansion coefficient.
A sister laboratory and kitchenware product is Corningware's Pyrex (TM) glassware featuring very high silica content, made workable by its boron content.
One of the methods of "disposing" of nuclear waste is by melting the radioactive products with suitable glass-maker compounds to tie up the fissile atoms, then pouring the resultant glass into corrosion-resistant, mechanically strong stainless steel tubes, capping them, and storing these "logs" underground in dry caverns; which can then be protected from access.
Pyrex has been cheapened:
Excellent range of info in a short space. Are you a technical writer?
Very old church windows have been observed to be thinner at the top and thicker at the bottom: slowly oozing down...
The glass in an old window will be thicker at the bottom than at the top due to the glass’s viscosity. Granted, the difference is slight and it doesn’t manifest until many years have passed, but glass is a liquid, albeit a highly viscous one.