Here is an image of the Dow and Nasdaq from Yaboo Financial. I have added a pale blue ("Support") band. Click on the image to enlarge.
Notice the pattern? The graphs tend to rise up above the Support Band, but suddenly come crashing down to it again. In the long term, the rate of growth is indicated by the slope of this band.
The Nasdaq tends to really go wild, rising to mighty heights. When it parts dramatically from the Dow, a crash is due.
As we enter 2015, we can see that a crash is now due. Both must fall, but the Nasdaq has the furthest to go. The spark that will light the fuse for this crash this time is the imminent rise in FED interests rates. ZIRP (Zero Interest Rate Policy) has been followed in the US since 2008 to spur economic growth. Now that the American economy is growing, American Interest Rates will rise, bringing down the price of shares.
The pattern is for share prices to fall much more quickly than they rise, so we can anticipate a dramatic fall in the coming weeks.