I believe it pushes up a huge pile of ashes, then reaches a crescendo that rolls on down the mountainside, likely in small increments.
It does push up and crumble again. What was visible in person (that doesn't show up in the pics) was a large 'tower' that was new last time since my earlier visit. This tower was evidently many stories tall and was destined to fall over. Again, it's hard to grasp the scale of it, even when you are looking at it.