National Public Radio: SCOTT SIMON, host: This is WEEKEND EDITION from NPR News. I’m Scott Simon. Travel across Europe is at a standstill for a third day after a volcanic eruption in Iceland has clouded the skies. Flights have been cancelled, airports closed, thousands of passengers stranded. Scientists in Iceland are keeping a close eye on a volcano that began erupting on Wednesday. Not only does the ash pose a risk for aircraft, but as NPR’s Joe Palca reports, the eruption can cause serious …