'Randomness and chaos': The invisible, unpredictable forces behind fatal rockfall

Scientist Daniel Shugar says images of the aftermath of Thursday's deadly rockslide in Banff National Park provide evidence of its cause — water flowing through the interior of the mountain.

"You can actually see some springs coming out of the cliff and actually coming out exactly from the scar itself," said the University of Calgary professor of geomorphology.

He described how water from a lake above the cliff at Bow Glacier Falls had been seeping through rocks for decades before it eventually provided enough force to dislodge a boulder, triggering the rockfall.

"That lake has existed since 1955," he said. "So over the last 70 years, the water from this lake (and the) glacier retreating has been trying to go downhill through the cracks. It essentially provided the pressure to dislodge the rock."

LISTEN | Geomorphologist offers insight into rockslides

While the forces may have been building for years, Shugar and other scientists agree it would have been impossible for Parks Canada to predict or prevent the massive rockfall.

"Yesterday was just a bad confluence of events where this chunk of rock essentially popped out of the cliff," he said. "And, you know, unfortunately, tragically, there were hikers down below."

Experts agreed that while evidence of previous rockfalls is easy to see, predicting exactly when they will occur is impossible.

Davide Elmo, a mining engineering professor at the University of British Columbia, said that looking at a rock face from the outside doesn't show what's happening inside.

"Some people might ask Parks Canada, why didn't you do anything about it," said Elmo, who also has a degree in engineering geology and is an expert in rock mechanics.

"Well, that kind of rockfall cannot be stopped."

He said the only thing officials can do is to tell the public about the risks when they enter an area that might be prone to rockfalls.

"We know they will happen. We don't know when they will happen," said Elmo.

Witnesses reported rumblings and stones moving before a slab of mountain broke loose and rained boulders on hikers below.