Avalanche on Echo Peak

We (party of 3 skiers and one splitboarder) were approaching the summit ridge of Echo Peak with the intention of skiing terrain on the northeast bowl. The last ~50 vertical feet to gain the summit ridge was quite steep, so we decided to switch to booting. One skier began booting up while the other 3 were transitioning from skinning to booting. When the first skier had hiked approximately 20-30 feet up the steep slope,  a wind slab suddenly released from above and propogated laterally for some distance. All four of us were caught and taken 20-100ft downhill. The skiier who triggered the avalanche traveled the furthest, and deployed an avalanche airbag. The other two skiers and the snowboarder were stopped by trees after being taken a short distance. The snowboarder was partially buried downhill of a tree. No injuries, one set of poles were lost.