At least four groups of riders were out in remote, mountainous terrain near McBride, British Columbia, when the avalanche struck at 1:30 p.m. (4:30 p.m. ET) Friday. Two people managed to activate rescue beacons -- a recommended emergency tool for those enjoying backcountry snow -- to alert authorities, according to the Royal Canadian Mounted Police
Two search-and-rescue technicians who happened to be snowmobiling in the area "were on scene almost immediately," the police said in a news release. They were able to rescue several members of the groups caught in the slide.
The deceased were all from Alberta. They were identified as Vincent Eugene Loewen, 52, Vegreville; Tony Christopher Greenwood, 41, Grand Prairie County; Ricky Robinson, 55, Spruce Grove; Todd William Chisholm, 47, St. Albert; and John Harold Garley, 49, Stony Plain.
Six people were take to a hospital; all have been released.
Officials don't know yet what caused the avalanche.
Rod Whelpton, who was snowmobiling in the area, said the avalanche was 700 meters (765 yards) wide.
Whelpton told reporters that he went out that day to have fun. He recalled the avalanche risk level being "considerable" -- in the middle of the danger scale.
"I went in believing it was a very safe, good area," he told reporters. "It was very much a normal day, a nice day."
Canada averages about 12 avalanche deaths a year, according to Avalanche Canada spokeswoman Mary Clayton. The vast majority of those -- about 10 annually, according to a a 2014 report by that province's Coroners Service
-- are in British Columbia. Most of those killed there tend to be from British Columbia or neighboring Alberta, and almost all of them are men.
Roughly 41% of those caught up in such avalanches were snowmobiling, 34% were skiing and 13.5% were heli-skiing -- flying by helicopter to a secluded spot and then skiing.
Avalanches can occur on their own or be triggered by humans.
That's seemingly partly the case with Friday's "very large, significant" avalanche near McBride, a village about 450 miles (740 kilometers) northeast of Vancouver.
Karl Klassen, warning service manager at Avalanche Canada, said this event "appears to be human-triggered," though weather and snow conditions played a factor as well.
"There are layers of concern in the snowpack in many parts of this region (and others)," wrote Klassen on his nongovernmental organization's website
. "And a fairly significant weather event added ran and snow to the snowpack over the last few days, followed by clearing and cooling.
"This may have produced stresses in the snowpack capable of producing large avalanches."
Clayton, from the same organization, said that the number of avalanche deaths in Canada generally has been trickling down -- a fact that can be attributed to better awareness and preparation -- despite more and more people going into the backcountry.
What makes Friday's incident unique is how many people died at once.
"When you have a lot of people killed in one incident, it can tell you a lot of things," Clayton said. "A lot of people were clustered together. A lot of people were exposed to hazards at the same time."