Rapidly warming oceans are cutting into the underside of the Earth’s widest glacier and posing a major sea-level-rise threat, startling new data and images show.

Using an underwater robot at Thwaites Glacier, researchers have determined that warm water is getting channeled into crevasses in what the researchers called ‘’terraces’’ — essentially, upside-down trenches — and carving out gaps under the ice. As the ice then flows toward the sea, these channels enlarge and become future potential break points, where the floating ice shelf comes apart and produces huge icebergs.