HOW'D THAT HAPPEN??

Bizarre, the dark surface of the crown is kind of striking...

RonL's observation about the dark/dirty crown wall has caused me to rethink.  Here's a simpler hypothesis that doesn't require random steam bursts.   

I've noticed many alpine meadows (esp. in the Olympics where there is lots of scree) that have miniature glacial 'eskers', sinuous gravel ridges 1-2 feet high and several hundred feet long, sometimes on top of the vegetation.  I think these must be formed in melt tunnels at the base of the Spring snowpack during heavy rain or very warm weather.  The avy location photos look pretty high on the slope for much runoff to form, but perhaps one of these subnivean drainages encountered a glide crack and filled it with a gravel slurry until the snowpack below broke loose?

Hmmmm, July 4, you say? I think a couple snowboarders with backpacks full of M-80s or fireworks, carefully placed could do that. And the perpetrators cleaned up the debris and carefully hid their tracks out of there - just to mess with park rangers' and TAYers' heads.

well, .. those cracks have been there a while, eh?  including the ones whose remnants are barely seen along the left edge of the slide, in the first magnified pic, and all in a decreasing radius from what would be the epicenter of the slumping snow, which gave way at one point as a wet slide due to localized subterranean heating, as evidenced by the small central and completely snow-free spot on the bed, pulling the snow from above, yet below the upper crack, with it as it moved a very short distance down slope, encountering firmer conditions and thereby jumping back onto the surface, leaving that hump at the top of the debris pile, and the rest sloughing according to fall line, moving the top couple of inches of snow - slush, really - along the perimeter, the same as a played-out wave will move the edge of seafoam inward on that wide, flat beach, demonstrating clearly the near liquid nature of a portion of that snowfield, set free by that single warm locus.

I think Silas wore that area out with too many laps!  But I'd guess some kind of thermal vent in that area.  Isn't there a face on Alpental that has some heating happen on a rock face, so it slides easy? 

just the type of spot silas would enjoy an adventure, esp. rockface, huh silas.
b

Hmmmm, July 4, you say?  I think a couple snowboarders with backpacks full of M-80s or fireworks, carefully placed could do that.  And the perpetrators cleaned up the debris and carefully hid their tracks out of there - just to mess with park rangers' and TAYers' heads.

Could have been...

Or it could just have been a real violent Storm... Lady . :

Maybe a glide crack filled with some water and it was isolated to just that area under the glacier and eventually it had enough torque to slide it down? That slide scares me in some strange way as it looks like it would not do that at all.