Consider a situation where a stock that was performing normally for a while crashes, say because news about a catastrophic development in the company become public. The share price drops from USD 85 to USD 30 during one hour, in what on the chart looks like a straight, steeply diving line, before recovering.
I have set a stop-loss selling order at 70 USD. When it gets triggered, analysis of the stock price graph will indicate that it's definitely going to plummet further before recovering.
As I and thousands of other market participants hurry to sell their stocks, a huge volume of orders is created. In order for my stop-loss selling order to succeed, someone must be buying them. But both automated systems and human traders should easily spot the "hopeless" situation and refuse to buy unless the curve starts to flatten. Even if we allow for some "irrational" market participants, they should not have enough buying power to soak up all the sellers' offers.
So who, and why, actually purchases stocks in the few minutes of an ongoing crash?
NB: A very similar question was asked here before. I consider my question not a duplicate because the other question was about week-long "crashes" and was asking "who is buying" more in the sense of "why would people be so stupid", easily being answerable by looking at daytraders and automated system working successfully on tiny margins and short timescales. My question aims more at a situation where both human and algorithmical market participants have hardly any time to act and it is clear that there is no upturn in sight for the next few minutes.