After taking 3-4 turns into Main Days, I saw huge cracks and sliding snow all around me. I cut hard skiers left and was able to get out from the main part of the avalanche. Thinking I was safe, I turned around to see what was going on. I quickly saw that the avalanche had propagated, and was running above me and towards me. I frantically kept skiing and was luckily able to get out of the runout zone. The avalanche was about a foot deep (new snow) but had propagated massively. In total it was probably 300 feet wide and the crown ran down the ridgeline about 400 feet. At the bottom, the avalanche had been funneled by a gully and there was a substantial amount of snow deposited.