A minuscule garbage company is suddenly one of the hottest stocks of the year.

Shares of Industrial Services of America ( IDSA - Get Report), a small Kentucky-based waste management firm, are up a cool 923% this year, rising almost 25% in early Monday trading.

More than 4 million shares traded in Monday's first 90 minutes, making it one of the most actively traded stocks on the Nasdaq. The frenzied early activity pushed the stock up $8.13, or 23%, to $43.40.

It's remarkable volume for a stock with just 1.6 million shares outstanding.

Industrial Services' surge follows only one piece of recent news: an announcement late last week of a 2-for-1 stock split. Trading in the stock has exploded in the past two weeks -- especially after the split announcement -- with the stock rising 450% in that period alone.

The surge in Industrial Services, a company that earned $668,000 last year, or 41 cents a share, defies easy explanation. Company officials could not be reached for comment on the trading.

One hedge manager, who doesn't own shares of the stock, said the trading was unusual and seemed out of the ordinary.

A Nasdaq official declined to comment on the trading.

In the past, investors have been known to buy shares of stock after hearing about a split, which technically should have no economic bearing on the shares. Postsplit appreciation is a trading pattern that occurred frequently during the stock market bubble and is one that continues to mystify market watchers.

Of course, a stock split doesn't change the value of a stock. An investor who owns one share of a $10 stock, simply has two $5 shares following a 2-for-1 stock split.

Some investors no doubt buy a stock that has announced a split on the theory that many retail investors don't understand the concept and they will be able to trade it as short-term momentum play.

Others contend that a stock split causes a short-term short squeeze, in which short-sellers -- traders who bet a stock will fall in price -- are forced to close out their short positions, a move that pushes a stock higher.

Only about 5% of the company's minuscule float is short interest, however.

Before this year, it's fair to say that most investors never heard of Industrial Services. Prior to Feb. 9, the stock often traded fewer than 10,000 shares on an average day. On some days, no shares traded hands.

The frenzied trading in Industrial Services comes at a time of peculiar stock movement throughout the small-cap universe.

Last week, TheStreet.com reported the big rise in shares of Vaso Active Pharmaceuticals ( VAPH), a small company with no profits, less than $100,000 in annual sales and seven employees. Shares of Vaso Active have risen 440% to $27, since a mid-December IPO.

Like Industrial Services, Vaso Active has only about 1.6 million shares outstanding and announced a stock split in the past few weeks.

Other small-cap stocks have surged on news of stock splits this year too, including Taser International ( TASR), manufacturers of a stun gun. In mid-February, the company's shares spiked 45% after announcing a 3-for-1 stock split.

Industrial Services wasn't the only small stock moving higher Monday with no good explanation. In early trading, shares of Unifab International ( UFAB - Get Report) doubled to $9. The stock of the producer of oil and gas platforms rose on little obvious news.

Like Industrial Services, trading in Unifab was brisk. Before noon, some 437,000 shares had changed hands, already a 32-fold increase over the stock's daily average.

It's too soon to say the market bubble is back, but some weird things are happening out there.