"There was no feeling of panic, more a concerted effort to protect my head and neck and be aware of what was below me, where I was heading and what I could do to slow and stop myself before I got to the more serious rocky outcrops."
Roberts lost both of his axes trying to slow his descent, and had to use his arms, hands, legs and feet to slow his speed.
"Fortunately I slid into a rocky outcrop on my left with a bit of a thump, which took some of the momentum out of my decent, resulting in a bit of a spin, but I could still look for opportunities below for a point to stop. It finished with a drop onto a bit of a ledge or hole where my pack and crampons took enough hold to stop me."
When Roberts finally came to a stop he was fortunately conscious. His first action was to check the camera was still attached.
"I knew I'd lost my glasses somewhere but I could see movement of someone below and gave them the thumbs up to show I was conscious and not too badly injured. I already knew there was some damage to my ankles which were fairly painful if they were moved."
His climbing companions raised the alarm and he was rescued 30 minutes later.
Elfyn Jones, a member of the Llanberis Mountain Rescue, told British Mountaineering Council the rescue team had just finished a training exercise in Llanberis when the call came through and the helicopter was just about to head off on a training mission.
"I think the key message here is that accidents do happen, but that Mark was well equipped, wearing a helmet, and that probably saved his life," Jones said.
"The other climbers in the area did exactly the right thing. His friend dialled 999 and asked for the police as soon as they saw the fall, and he was lucky in that two members of the mountain rescue were climbing nearby."
Roberts said he is "annoyingly immobile and bruised, but mentally fine".
"I'm getting used to injecting myself with blood-thinning drugs to prevent clots forming, and planning how to get my fitness back once the bones have healed and the cast and support come off."
- nzherald.co.nz