did not want to hijack an existing thread.

the leader of any hiking group has to be boringly aware of many possibilities.

this fellow was: aware

a 2:27 video. give it to 50 secs.

Wow, eye opening. My first thought was why are they crossing a river of gravel -- obviously to get to the other side. That said, note how the peeps crossing stand back on the far side until it's their turn and once across they expedite up and out of the way. Also note that when the call is given no one hesitates. They knew this could happen and they knew the danger.

Impressive!

The guides obviously were well aware of the hazard, and handled the crossing with that in mind. I couldn't tell from the video (and my Spanish is poor), but I'll bet they had someone posted as a lookout in a spot they could see upstream and yell a warning if a big one was coming down.

In organized avalanche rescue/recovery, if there is even a slight chance of another slide coming down the same path, it is standard practice to post a safety lookout. An escape route is also clearly defined. Everyone working on the debris pile knows if the lookout yells, instantly drop what you are doing and run like hell on the escape route. (Note that if there is a significant chance of another slide, recovery ops probably will not occur until control work is done to eliminate the additional hazard.)

WOW! I'm not sure I'd be brave enough to do that hike.

It didn't look like fun to me.