Four of us friends went down to Mosaic walls and I set off Rollerwall whilst my other two friends were at the bottom waiting for me to get high enough so they could start their route, Mural Landscape, which was adjacent. Half way up the pitch I pulled into a niche which is the belay for Mural Landscape, as I was rocking up into it the hold I used started moving only to noticed an entire block becoming detached. I soon was falling backwards with a fridge-sized rock following me. It wrapped around one of my ropes which got pretty much cut, luckily the other rope held my fall and block flew past me only leaving me with mild contusions and a hard slam. But as I was coming to halt I looked down to see the great block exploding in many pieces and all my three friends running for cover. As soon I had stopped i looked down again and I could see one of them crushed into a boulder gap. I got lowered down and quickly assited her, she was like a rag doll being rammed into a hole, it was horrific. We had no choice but to pull her out as the way she was she would have chocked. She was unconscious and me and my climbing partner ran to call the rescue and her boyfriend stayed with her. She looked dead. Once we had call rescue we ran down again to see she was breathing and moving, but in an out of consciousness. I checked her body and there weren’t major injuries, but the back of her head had a major trauma. They had helmets with them but they weren’t wearing them. The rescue came fairly quick and direct to our point as we gave them coordinates (useful thing in crag pages in the CC guidebooks) and because we had assesed her she was airlifted immediately without putting her on a stretcher. An air ambulance was waiting at the top. Once stable she was moved to Cardiff hospital. She later died in hospital. The head trauma would have been prevented had she been wearing her helmet. All other injuries were pretty minor considering the size of the event.