The long-dormant Chaiten volcano blasted ash some 20 miles (30 kilometers) into the Andean sky on Tuesday, forcing the last of thousands to evacuate and fouling a huge stretch of the South American continent. A thick column of ash climbed into the stratosphere and blew eastward for hundreds of miles (kilometers) over Patagonia to the Atlantic Ocean, closing schools and a regional airport. Citizens of both countries were advised to wear masks to avoid breathing the dangerous fallout. Chilean officials ordered the total evacuation of Chaiten, a small provincial capital in an area of lakes and glacier-carved fjords just six miles (10 kilometers) from the roiling cloud. More than 4,000 people were evacuated over the weekend and 350 more headed out Tuesday.