This image shows a portion of Lethe Vallis, an outflow channel that also transported lava. It’s one of only a few places on Mars where pristine-appearing landforms have been identified. The channel formed by catastrophic floods, during which it produced the prominent crater-cored, teardrop-shaped island in the middle.
This image was taken by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter.
According to NASA, both the island and the fluvial dunes were formed by these extreme floods and their size is an indicator of the enormous discharges required to create them. The margins of the channel also show the terminal front of a pristine lava flow unit that inundated the channel from the south and the dunes show the remnants of another older lava flow. The top of the island displays polygonal patterned ground texture, which is a characteristic of periglacial processes in ice-rich ground.
Scientists believe the dark materials from the channel and island walls are probably dark sand being eroded from an underlying horizontal basaltic (lava) layer. The crater at the core of the island has elongated dunes and reticulate dust ridges inside.