William sent in a link to a video of catastrophic moving water, some 2 million cubic metres spilling down towards the village of Chukhung in Nepal last year (2016) – go to https://eos.org/articles/glacial-outburst-flood-near-mount-everest-caugh…
Within a glacier water moves in conduits (or drains). The scientist describes it as something like Swiss cheese (lots of holes and canals). Sometimes the conduits become blocked by ice or by rock debris, from gravel to boulder size, or just lots of sand. Water pressure then builds up behind the dam until the water is eventually released – dramatically in this case. The flood rushed down towards the village. Luckily, as a result of a recent earthquake in the Himalayas a rock wall had been built to defend the village – and deflected the water. No one was killed.