Why do some of Triton’s lake-like features have terraced edges?

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Moons of Neptune: Triton — Triton Image of Triton, Neptune's largest satellite, captured by a camera aboard Voyager 2, 1989.

The terraced edges observed on some of Triton’s frozen, lake-like features are likely the result of multiple, successive melting events. In each of these episodes, a smaller patch of ice was involved than in the previous one, creating the stepped appearance.

While these terrace cliffs can rise more than 1 km (0.6 miles) high, nitrogen or methane ice is not strong enough to support such structures at Triton’s extremely low surface temperatures without slumping. Consequently, scientists hypothesize that the underlying material of these features is water ice, which behaves more like rock under these conditions. Although direct spectral evidence of water ice is absent, it is believed that a thin veneer of nitrogen or methane ice may be masking its presence.1