A new video published by the New York Times on Thursday reportedly shows a group of Mount Everest climbers less than an hour before they were swallowed up by a deadly avalanche last month.

“Shot by Ang Kaji Sherpa, the footage shows several climbers ascending the Khumba icefall on steep ladders. Ang Kaji explains to a colleague that the group is experiencing some trouble because the route hadn’t been created, according to the Times’ translation in the video. About 30 minutes after the interaction, the group was hit by a massive wave of snow and ice,” the Huffington Post reports.

More than a dozen Nepalese guides were killed in the April 17 avalanche on the world’s tallest peak.