The Icelandic volcano that has paralyzed European air travel for a week looked to be calming down, until it spit another huge ash cloud into the sky Monday. The cloud, which Eyjafjallajokull shot 15,000 feet into the air, was moving toward the United Kingdom and could possibly worsen stranded passengers’ travel woes. Earlier Monday, authorities had said travel restrictions would be partially lifted. (Europe would be divided into three zones, one in which airports stay closed, one allowing all flights and one allowing only certain flights.) But after the latest volcanic blast, Northern Irish airports may have to stay closed, though Scottish ones will reopen Tuesday morning. London will remain closed. So far, the volcano has cost airports $184 million, and thousands of travelers remain stranded.