A pile of Bitcoins minted by Software engineer Mike Caldwell on April 26, 2013 in Sandy, Utah © George Frey, Getty Images

As the Federal Reserve tightens policy and emerging-market demand cools, we are going to see plenty of unsustainable growth models fail to meet Wall Street expectations and slowly come apart at the seams.

Or, if you prefer the more panicked parlance of the blogosphere . . . some bubbles are about to get popped.

Not all of these bubbles will, of course, burst in quick or dramatic fashion. Sometimes bubbles simply deflate, either steadily or slowly, until all the air inside is gone and only the lining remains.

But regardless of the pace, the risk posed by these five bubbles is fairly clear -- and investors should start to prepare accordingly.

1. Emerging markets

Thailand, Indonesia and the Philippines saw big contractions in their stock markets in June. At the time, the narrative was that investors were withdrawing money to deploy back in the U.S., but now the story has turned into a tale of China's slowdown. As evidenced most recently by weak manufacturing data, China is seeing serious challenges, and that is hurting growth potential in these markets by proxy.

Elsewhere, you have once-resilient regions like Brazil and Turkey roiling with political unrest, rattling stocks in these regions as well.

The results have been ugly indeed. Consider the iShares MSCI Brazil Index ETF (EWZ) -- a massive fund with $5.6 billion in assets and top holdings that include mega-caps Petrobras (PBR) and Vale (VALE). This Brazil ETF has lost about 25% in just two months.

It's tempting to make excuses about short-term political movements or the long-term potential of an emerging middle class in these markets. But recent turmoil shows that emerging markets in all corners of the globe are facing serious challenges.

2. Junk bonds

Junk bonds have had a phenomenal run during the past few years as a low-interest-rate environment, coupled with a hunger for yield among investors, added up to insatiable demand.

But now the winds are changing. After junk-bond yields hit an all-time low of under 5% in May, there was simply nowhere left to go but up, especially thanks to talk of tighter policy at the Federal Reserve. Junk yields already have rallied to a 2013 high at more than 6.3% in short order, with related high-yield bond investments like the SPDR Barclays Capital High Yield Bond ETF (JNK) giving up over 5% . . . even as the market has rallied since mid-May. Subsequent rises in yields will push prices down even further.

And more broadly, nations and corporations dependent on easy money -- which includes some of the emerging markets just mentioned -- will have to figure out a way to borrow with much higher rates and interest payments. That could mess with the markets at many places down the line.

Last but not least, if investors simply are looking for a modest return of 5% but begin to find it in much safer instruments like investment-grade corporate bonds in a higher-interest-rate environment . . . well, that big sucking sound will be all the air deflating from the junk-bond bubble as folks move their money to other investments that deliver yield with less risk.

3. House flipping

I remain convinced that, broadly speaking, housing is in a sustainable recovery. But I can't help but notice the return of house-flipping seminars, bidding wars and the idea that a house is an investment that can make a quick profit with minimal risk.

Consider that house flipping in California is back to 2005 levels, according to a recent Wall Street Journal report. Not good.

Thanks to very tight supply and weak demand, the dynamics have strongly favored sellers -- for now. That has allowed speculators to creep in and start treating real estate like a short-term investment again.

Properties across the U.S. differ widely, and each area has its own challenges and opportunities. But it is increasingly clear that the areas hit hardest by the housing downturn could be ground zero for another real estate bubble should the flippers throw in the towel. Consider that more than 50% of real estate transactions in Las Vegas, for instance, continue to be all-cash purchases, and a staggering 1 in 10 sales are to foreign investors.

Regions that have stabilized thanks to a slowly mending economy and organic demand are one thing. But house-flippers in speculative markets better watch out.