Heavy mud, lake water and flying boulders swamped the hut, trapping Pike and crushing his leg.
Christie was later awarded the New Zealand Bravery Medal for saving his friend. He had walked an hour down the slope to alert emergency services.
Pike had his right leg amputated after being airlifted to Waitako Hospital by helicopter.
Tracy insisted her boy "never had a negative moment" during his long and painful recovery. His attitude had been "outstanding'' throughout, she added.
She said William wasn't sure whether he would be able to make it all the way to the summit today because his remaining leg still isn't back to full strength.
But she believed that the schoolkids on the climb - nicknamed Pikelets - would spur him on.
"William is very fit, swims four times a week and does a lot of bush walking, but this is going to be real test for him,'' she explained.
"He joked beforehand that James can carry the load for him and he'll just go up with just his poles."
Tracy said she texted both men good luck messages before they set out on the final stage of climb early this morning
"I said to William 'this is your day, just go for it' and to James I said 'thank you for being the best mate'."
Tracy also said that a large piece of volcanic rock believed to have struck William has pride of place in her Forrest Hill garden. It serves as a permanent reminder of his dramatic brush with death.
"I sometimes just go out there and look at it. We also have a small jar filled with lahar dust from The Dome and feathers that came from William's down jacket that had to be cut off him when he was rescued.
"William doesn't bother too much about these things but they are nice for us to have.''
Pike and Christie stayed last night on the mountain and planned to get to the summit today.
"If they get to The Dome, I'm sure they will both have a quiet moment to themselves, to remember just what happened," Tracy added.
