Complex sentence: A large slab of ice, about 100 meters wide, broke off a ridge causing a mass avalanche with several branches of snow about 400 meters wide, engulfed 13 of the skiers in a steep sector of the valley.
Split into simpler sentences: A large slab of ice, about 100 meters wide, broke off a ridge causing a mass avalanche. Several branches of snow about 400 meters wide, engulfed 13 of the skiers in a steep sector of the valley.