Market cap and other useless metrics.

It does depend a lot on how much of the circulating supply is actually in circulation. There are millions of bitcoins which are effectively not in circulation because of lost keys, bad transaction address entry and other issues. The market price of a coin in the short term is determined by availability on the markets and demand. If there are only 50 coins for sale across all the markets and 1 is on sale for $10 million above the rest of the $0.1 sell orders and someone buys 0.00000001 of that market order the "price" will be $10 million as far as the market data is concerned. Market capitlisation and circulating supply are yet another massively inaccurate measure we use to estimate things. Exciting isn't it?

If the price spikes on any coin some folk will be shaken out of their desire to hold in their wallet so there will be an influx of market supply from storage. This should lead to a dip in price but the holders may well decide to set their sell orders above current "market price" and so the price can continue up from my $10 million as long as there are people looking to buy. Who wants to sell a coin for $0.1 when they paid $10 mil for it but they don't want to pay $10 mil again so they populate the order book with lower than $10mil but not too much and suddenly you have price support. if people continue to buy, you get bitcoin's meteoric rise.