The specific geological cause is not yet clear.

We do know that a glacier substantially collapsed.

What contributed to the amount of water in the debris flow isn't clear. Speculation, from trained geologists, is that the friction of the glacier flow itself contributed to melt. I'm speculating that recent rains or higher temperatures might have contributed to melting on the glacier (and have seen some commentary speculating about this).

Speculating on my part: There might also have been accumulated water below the glacier, liberated by the ice flow, or perhaps groundwater which was evacuated along with other material. Events seem to have precipitated too quickly (roughly 7 minutes from galcial collapse to Gyirong Port inundation) for the collapse to have formed, then broken, a dam on tributary waterways upstream of the port.

GLOF is a recognised threat, but this event seems to have been at best only partially explained by that, and may be an entirely different mechanism. The follow-on studies should be fascinating, in the way that horrific disasters often are.

That all tracks - good additional comment.

> Speculation, from trained geologists

Probably about on par with speculation from trained geophysicists I'd warrant.