From Bubble to Depression?

From Bubble to Depression?
(Source Wall Sreet Journal)
Bubbles have been frequent in economic history, and they occur in the laboratories of experimental economics under conditions which -- when first studied in the 1980s -- were considered so transparent that bubbles would not be observed.
We economists were wrong: Even when traders in an asset market know the value of the asset, bubbles form dependably. Bubbles can arise when some agents buy not on fundamental value, but on price trend or momentum. If momentum traders have more liquidity, they can sustain a bubble longer.
But what sparks bubbles? Why does one large asset bubble -- like our dot-com bubble -- do no damage to the financial system while another one leads to its collapse? Key characteristics of housing markets -- momentum trading, liquidity, price-tier movements, and high-margin purchases -- combine to provide a fairly complete, simple description of the housing bubble collapse, and how it engulfed the financial system and then the wider economy.
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http://online.wsj.com/article/SB123897612802791281.html