Electronic trading – and specifically computer-driven algorithmic trading – may be to blame
“Computers are deciding when to buy and when to sell. When the herd mentality gets automated, the stampede [in and out of markets] gets turbocharged.”
Some analysts argue that while algos do not produce volatility, they can amplify existing volatility considerably.
Overall an fascinating article and worth a read
http://www.ft.com/cms/s/0/c9814b98-a5e7-11dd-9d26-000077b07658.html