Alts sometimes move by huge percentages, the gains (and losses) can be several hundred times the moves in bitcoin trading. The problem is that it is risky - if you buy at the wrong moment in the pump, you can end up a bagholder. And it is also hard to know in advance which alt is going to be pumped.
However there is a low risk way to participate in altcoin pumps - lending bitcoin on Poloniex.
Most pumps are funded with borrowed bitcoins
Typically a speculator will see that a coin like Monero is surging because of some development or news and Fear Of Missing Out (FOMO) takes hold. They will pile in to buy, using margin trading where they are borrowing bitcoins. They hope that their return from the pump will be bigger than the interest they are paying.
The way to profit from this is to be on the other side, lending the bitcoins out. The risk from lending coins on Poloniex is practically nil - Poloniex acts as a middleman, automatically liquidating traders who are underwater, and returning coins to the lender with interest. When a pump is on, you can typically get 0.02% to 2% interest per day, which is an annual return of 7.5% to 1300% if you can keep your coins lent out the entire time.
Of course in practice, your money won't be lent out for the entire 365 days of the year, and Poloniex takes a 15% fee out of your interest earned. And you won't make as much as you would have if you were participating in the pump yourself, but your risk is very low and you don't have to know in advance which coin is being pumped.
Set your loan offer at a decent rate (0.02% or more, don't set it too low) , and lend for a long period (say 20 days). What often happens is that the borrower holds on, hoping that the market will turn, so the loan will continue to run to teh end of the term. If you lend for 2 days, you automatically get your money back and the borrower who still has their position open, will have their loan supplied by the other open loan offers.
Shorters will borrow alts
When pumps happen, people arn't just going long. There will be some speculators going short - they are borrowing the alt with interest, and selling the coin, hoping to buy back lower (at which point they repay the loan and pocket the difference).
Altcoin lending isn't as profitable as bitcoin lending. For a start only a few alts are available for margin trading - Ether, Monero, Doge, Dash, Litecoin, Bitshares, Clams and Factom. And the interest rates you can charge will be lower.
But if you hold any of these coins and are a bagholder (you participated in a pump in the past and bought too high but don't want to sell at a loss), you can recoup some of your losses by lending the coins out. Over time the interest you earn from the lending should reduce the loss you incurred by purchasing the coins too high
You won't make huge amounts of money from Bitcoin lending on Poloniex. But you won't make losses either. No matter what happens, thanks to the interest earned, you should end up with more bitcoin than you started with. That is to say, you will end up with more coins than if you just stored them in your wallet.