SANTIAGO - A volcano dormant for decades erupted in south-central Chile on Saturday, belching an ash cloud more than 6 miles (10 km) high that blew over the Andes and carpeted a popular ski resort in neighboring Argentina.Fanned by winds, ash darkened the sky in San Carlos de Bariloche, Argentina, a government official there said, adding the city's airport had been closed.The eruption in the Puyehue-Cordon Caulle volcanic chain, about 575 miles (920 km) south of the capital, Santiago, in Patagonia also prompted Chilean authorities to shut a heavily traveled border crossing into Argentina.Chile's government said it was evacuating 3,500 people from the surrounding area as a precaution. Officials said the volcano was spitting molten rock, but there was no visible lava flow.It was not immediately clear which of the chain's four volcanoes had erupted because of ash cover and weather conditions. The chain last saw a major eruption in 1960. Local media said the smell of sulfur hung in the air and there was constant seismic activity."The Cordon Caulle (volcanic range) has entered an eruptive process, with an explosion resulting in a 10-kilometer-high gas column," Chilean state emergency office ONEMI said.It was the latest in a series of volcanic eruptions in Chile in recent years. Chile's Chaiten volcano erupted spectacularly in 2008 for the first time in thousands of years, spewing molten rock and a vast cloud of ash that reached the stratosphere. The ash also swelled a nearby river and ravaged a nearby town of the same name.The ash cloud from Chaiten coated towns in Argentina and was visible from space. Chile's Llaima volcano, one of South America's most active, erupted in 2008 and 2009.