EFF/KRF: The market turmoil is caused by some combination of (i) quickly fluctuating changes in expected cashflows (future profitability), and (ii) variation in investor risk aversion that leads to variation in expected returns (the discount rates for expected cashflows). Both responses can be rational. In short, a change in volatility, by itself, says nothing about market efficiency. Of course, it is interesting to ask why the volatility of expected cashflows and expected returns increased so much, but that requires a much longer analysis.
Eugene Fama and Ken French are members of the Board of Directors of the general partner of, and provide consulting services to Dimensional Fund Advisors LP.