Rather, the entire front face of a glacier at high elevation sheared off, likely millions of tonnes of material at least, crashed down a steep runnel, slammed into the opposing slope on the other side of the valley at the bottom, made that partially collapse, dammed the river for several minutes, and then all descended at high speed as the dam failed, with the results we see.

Some reportage is still saying there was an earthquake - there wasn’t - the landslide itself was the source of the seismic waves.

https://earthquake.usgs.gov/earthquakes/eventpage/us7000tbwb...

https://en.wikipedia.org/wiki/1970_Huascar%C3%A1n_debris_ava...