Richard Mansfield, a mountain guide who has worked in the area for 20 years and lives close to the Bossons glacier, said:
"I don't know exactly where the accident happened but all the trails on the north side of the valley are covered in snow. The footpaths usually don't get that many people out at this time of year because they are much more difficult to navigate, although yesterday was a beautiful sunny day."
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Nearly 38,000 runners will hope to complete Sunday's London Marathon making it the biggest event in its 35-year history.
Rain across central Britain with longer, intense downpours with thunder in places this evening. A lucky few will stay sunny and dry.
Planning on going to the London Marathon tomorrow? Read our handy guide first!