ETF trading volume was very quiet on Friday but it could be just the calm before the storm as investors prepare for key elections in Greece and next week’s Federal Reserve meeting.

The Greek ETF, Global X FTSE Greece 20 (GREK), was rallying for a third straight session on heavy trading volume Friday as voters prepare to return to the polls this weekend after the inconclusive election in May. If leftist party Syriza prevails, investors are concerned Greece may end up leaving the euro.

U.S. equity ETFs were on track to rise for the second week in afternoon trading Friday. The S&P 500 was poised for a weekly advance of 0.9%, the Dow added 1.4% and the Nasdaq Composite lagged with a slight 0.1% gain.

This week’s top gainer in ETFs was U.S. Natural Gas Fund (NYSEArca: UNG). The fund surged 15% Thursday after supply grew less than traders had expected.

“The market was wrong-footed ahead of the EIA number and the new shorts that piled in have turned and covered,” said Eugene McGillan, a broker and trader with Tradition Energy, in a CNBC report. “Now we’re triggering fresh technical buying.”

Emerging market ETFs and particularly BRIC funds were strong this week, led by China and Russia. Brazil and India round out the so-called BRIC countries.

Conversely, several commodity ETFs lost ground this week. The steepest decliners included funds tracking grains, agriculture and oil.