Comment by ANH

There have been maybe three such events in the 21st century (glacier or landslides producing more than a magnitude 5 quake), and none of them have happened in an area like the Himalayas. The other two were in Alaska on Mt Steller in 2005 and the Lamplugh Glacier in 2016, neither of which produced massive downstream floods.

It usually takes entire icebergs calving off to produce such seismic events and intense monsoons to create such flooding.

Anticipation is one thing, effective response in the seconds before disaster strikes is quite another thing. This might not have been an absolute black swan, but even with foresight it is challenging in the extreme to avoid risk.

I've been reviewing what coverage I can find of the present event in Nepal/China, in context with Section 5.1, "Comprehensive approach to disaster risk management", of TFA.

It seems that what would be required would be:

- Active surveillance of glacial lake formation.

- Active mitigation of glacial lakes, reducing risk.

- Warning and response infrastructure, procedures, and protocols along the likly flood path.

From video of what I presume are among the worst-hit areas (see: <https://twitterwebviewer.com/?tweet=2092542957060841592>), there appear to have been at best a few seconds of warning. Very robust structures are demolished virtually instantly. Even had people been sheltering within those structures, or headed up-slope above the water flow, either structural integrity would prove insufficient, or response time inadequate to reach a safe elevation above the debris flow. The latter problem is compounded by what appears to be an extraordinarily strong air blast (likely hurricane-strength or greater) as well as massive amounts of airborne debris, much of it rock.

Terrain is severely constrained in the region, and the only buildable regions are in river valleys themselves. The Gyirong Port border crossing is located deep within a river channel, and despite robust construction simply could not survive the event.

See:

<https://en.wikipedia.org/wiki/Gyirong_Port> (Wikipedia article on the port.)

Map / satellite view: <https://www.google.com/maps/@28.2792579,85.3752907,1341m/dat...>

(Take a few minutes to examine the region around the port itself ... there are several communities and businesses all well within the disaster zone, and I suspect that obliteration to those matches or exceeds what was captured on video at the crossing itself.)

From the first video at this Twitter post, a camera situated roughly 20m above the base terrain did not survive the event (though it transmitted for roughly a minute).

A second camera (I believe near the same location) shows similarly catastrophic damage, and no chance for anyone at base level to climb to a safe elevation before being overtaken by the debris flow.

As the Cowboy Junkies said:

  But if there's on thing in my life
  That these years have taught
  It's that you can always see it coming
  But you can never stop it

Anticipation isn't sufficient. Other than entirely abandoning such locations during all periods of high risk, loss of life is likely, and catastrophic property and infrastructure damage inevitable.

<https://twitterwebviewer.com/?tweet=2092542957060841592>