Ninnis fell through a crevasse , and his body weight is likely to have breached the snow bridge covering it .
Mertz was skiing and Mawson was on his sled with his weight dispersed , but Ninnis was jogging beside the second sled .
Ninnis fell through a crevasse , and Mawson 's body weight is likely to have breached the snow bridge covering it .
Mertz was skiing and Mawson was on his sled with his weight dispersed , but Ninnis was jogging beside the second sled .