As I had suspected, "avalanche" has a much broader definition than that supposed by many in these parts. In my hometown, snow avalanches are nonexistent, and we use that word to refer to what others may call a "rockslide," or "falling rock." Here is definition 1 from webster.com:
1 : a large mass of snow, ice, earth, rock, or other material in swift motion down a mountainside or over a precipice.
So yes, the falling ice that rained down on you, gravy, H.A.Hawks, Sir gawain, BamaBeau, Skar, et. al, could conscionably be called an avalanche. Just glad to know you guys are all faring fine, as that little picnic could have ended in the obliteration of a serious chunk of Board readership.
- Norman Osborne