The big and broad selloff in the stock market is sending the VelocityShares Daily 2X VIX Short-Term exchange-traded note tvix soaring 30% on very heavy volume, and on track to close at a three-month high. Volume was 84.8 million shares in afternoon trade, more than four-times the full-day average and enough to make the ETN the most actively traded equity security on major U.S. exchanges, according to FactSet. The ETN is designed to deliver double the gain of the Barclays iPath S&P 500 VIX Short-Term Futures ETN VXX, -0.08% , which is up 15%. The rally in the volatility measures comes as the Dow Jones Industrial Average DJIA, -0.87% tumbles 544 points in afternoon trade, after plunging 666 points on Friday.