LIVEBitcoin does not “dump” — neither does it “pump.”
Price manipulators first pump and then dump bitcoin. This allows them to push the price up, sell high, then drive the price down so that they can again buy cheap.
Bitcoin (and, to an extent, all of the crypto currencies) are rather thinly traded. This allows large price jumps with relatively small turnover in units.
Manipulators love thinly traded commodities, and never more so than when they acquired the commodities at very low prices. Many of the ‘whales’ of crypto acquired their Bitcoin at under $20 per unit. They can throw a few thousand units into the ‘sell’ bucket without too much concern over what price they get for it, even if they’re losing. If they can control the market price, they can make it all back.
If memory serves, this function is described in “Liar’s Poker” when the author explains how traders stretch their positions to get control over the pricing.