Fresh slab on old hard layer. Fractures in snow shot back about 150' over top of two more riders.

Fog, snow and disorienting flat light put a rider not familiar with area in dangerous position. I called him back on the radio but he did not hear and continued. He stopped and radioed back it looked ok but flat light was so disorienting he couldn't see how steep it was ahead and below. I began to follow knowing it may be bad spot but also disoriented so stayed back 80'. I looked over my should behind at next rider back about 80' behind and when I looked back in front rider was gone. So hard to see anything but saw the fractures above me and a slide right where he just was. Called out avalanche gogogo on radio in case it was behind him and hadn't seen it. He said he was instantly swept and turned face down head down. Arms pinned and unable to deploy air bag. He shook himself free within seconds of stopping and radioed back not to follow. Myself and other rider should have deployed our air bags then turned around the way we came. Instead we made sure air bag handles were at ready and moved one at a time back on our tracks. Rider that got carried caused two more smaller slides after digging out his bike and exiting straight down and out. Fog was so bad we could barely see the slides as we circled around and out so no pictures taken.