MEDAN, Indonesia—A rumbling volcano on Indonesia’s Sumatra island on Wednesday shot billowing columns of ash and hot clouds down its slopes. The ash released by Mount Sinabung in North Sumatra province reached more than 4,500 meters (14,760 feet) into the atmosphere, and an avalanche of searing gas clouds blew 1 kilometer (0.62 mile) to the east and southeast, Indonesia’s Volcanology and Geological Hazard Mitigation Center said. There were no casualties from the afternoon eruption, said Armen Putra, an official at the Sinabung monitoring post, and an alert has been maintained at the second-highest level. The 2,600-meter (8,530-foot) mountain has been rumbling since last year and villagers were advised to stay 5 kilometers (3.1 miles) from the crater’s mouth. They’ve been warned about lava while authorities were closely monitoring sensors that picked up increasing activity in recent weeks. The last such eruption was in early May, when ash fell on nearby …