From The Market Ticker:
...Nobody - and I do mean nobody - is talking about what this sort of volume pattern means. Well, I will: this is the sort of pattern that precedes an all-on equity market collapse. It strongly implies that the only volume support that the market has is from "hot money" speculators. Lest you think this is sustainable let me point out that just a few weeks ago the very same so-called "commentators" said the same thing about China's market. Here's what happened:
(Go to MT for larger view)
The white box down below is the target on the break downward out of that flag last night - the top of the box is the critical "must hold" level from the first retrace off the bottom and the bottom of the box being the the start of the entire move. If they're lucky the market holds around the 250-275 level, but I wouldn't bet on it....