Frazil ice has also been demonstrated to form beneath temperate (or "warm-based") glaciers as water flows quickly downhill and supercools due to a rapid loss of pressure. This "glaciohydraulic supercooling" process forms an open network of platy ice crystals that can effectively trap silt from the sediment-laden water that flows beneath glaciers and ice sheets. Subsequent freezing and recrystallization can result in a layer of sediment-rich ice at the base of the glacier which, upon melting at the terminus, can result in significant accumulation of sediment in moraines. This phenomenon has been verified by elevated concentrations of tritium — produced by nuclear weapons testing and therefore almost entirely absent in ice frozen before 1945 — in the basal ice of several glaciers (signifying young ice) and the observation of rapid growth of ice crystals around water discharge vents at glacier termini.