ANCHORAGE, Alaska—Residents of a suburb of Anchorage in Alaska were ordered on Sunday to evacuate a mountainous area after one massive avalanche buried a road and another huge slide was considered imminent. Anchorage Mayor Dave Bronson issued the evacuation order, citing “a grave and immediate threat to the health, safety, and welfare of the citizens” in the affected area at Eagle River, on the city’s outskirts. The avalanche roared down a mountainside shortly before midnight local time on Thursday (0800 GMT) covering the main road with a snow layer up to 80 feet (24 meters) deep. But only about half of the snow in the unstable slide zone was released then, and a secondary avalanche is considered certain, local officials said. “If we have an uncontrolled release at an unknown time, that could result in the loss of life. We want to do everything we can to prevent that,” Anchorage …