Presented with little comment aside to note that based on a tweet, the 'deeply liquid' US equity market collapsed instantaneously as all those liquidity-providing 'algos' jumped ship...
The lower pane shows the market depth disappearing courtesy of Nanex [4].
[5]
The S&P tested down to yesterday's close filling the gap perfectly...
[6]
The good news, if indeed this was merely a test for "the big one", is that everyone managed to sell ahead of everyone else. Right?