Why are Triton’s tall terrace cliffs thought to be supported by water ice?

Triton’s tall terrace cliffs, which can rise more than 1 km (0.6 mile) in height, are thought to be supported by water ice because nitrogen or methane ice—the primary components of Triton's surface—lack the structural strength to support such features at the moon's extremely low surface temperatures without slumping.1

While there is no direct spectral evidence of water ice on the surface, scientists believe it forms the underlying material of these structures because it behaves in a much more rocklike manner at these temperatures. It is hypothesized that a thin veneer of nitrogen or methane ice may be masking the spectral signature of the water ice beneath.1