An American mountaineer went missing Monday after appearing to ski into a crevasse while descending a peak in Nepal. Hilaree Nelson, 49, summited Manaslu, the world’s eighth-tallest peak on Monday morning alongside her climbing and romantic partner, Jim Morrison, and three Sherpa guides. Around 15 minutes after they attached skis and began descending the mountainside, one of the guides radioed the expedition organizer with the message: “Big problem.” It appeared that Nelson had skied into a 2,000-foot crevasse; it’s not known if the mother of two from near Telluride, Colorado, survived the fall. After weather conditions frustrated search efforts, the expedition company planned to send a helicopter to look for Nelson at first light on Tuesday. But Bigyan Koirala, a government tourism department official, said a successful rescue was unlikely. “Based on the briefings and difficult terrain, it’s really hard to say whether we will be able to rescue her alive,” he said.