Click for full image.
Cool image time! The photo to the right, rotated, cropped, reduced to post here, was taken on December 3, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).
The title given to this image by the MRO science team is “Upstream Edge of Crater in Athabasca Valles.” The crater itself is a pedestal crater, uplifted from the surrounding terrain because it was more resistant to erosion.
The material to the east of the crater’s rim definitely appears to have flow characteristics, but is it wet mud, glacial ice, or lava?
To figure this out we need as always some context. The latitude, 8 degrees north, immediately eliminates mud or glacial material. This location is in the dry equatorial regions of Mars, where no near surface ice has yet been found. Thus, the flow features are likely hardened lava.
What direction however was the flow? Was it flowing to the north, widening as it moved past the pedestal crater? Or was it to the south, narrowing as it pushed past that crater? To answer this question we need to widen our view.
Click for full image.
The image to the right, rotated, cropped, and reduced to post here, was taken by MRO’s context camera on March 31, 2012, and shows this entire crater plus the surrounding region. The white rectangle indicates the area covered by the photo above.
The visual evidence, though still somewhat uncertain, suggests the lava had been flowing from the northeast to the southwest. For example, the teardrop shape of the aprons around both craters both suggest the flow was to the southwest. Furthermore, as the flow moved south it pushed through a gap in a ridge to flow to the south and southeast as well. The mesas in this area also have shapes that suggest the flow is to the south.
The overview map below tells us that this flow is near the head of what scientists have labeled the Athabasca Valles flood lava, as indicated by the dark blue area. According to this 2008 paper [pdf]:
Athabasca Valles is an outflow channel system located in north-central Elysium Planitia. It emerges full-born from the westernmost major fissure segment of the Cerberus Fossae, stretches southwest for 300 km, and empties into the Cerberus Palus basin. Previous work has shown that, despite the erosional appearance of its gross morphology, the entire channel system (including its banks) is coated with a veneer of lava. The lava is exceedingly thin in proximal Athabasca Valles and gradually thickens in the downstream direction, transitioning from a material unit that drapes the substrate topography to one that submerges it near the terminus of the channel system.
The most straightforward interpretation of these observations is that a fissure eruption at the head of Athabasca Valles flooded the down-slope terrain with lava, and then, as the eruption waned, the lava receded from the channels and drained downstream into Cerberus Palus where it ponded.
Athabasca is also thought to be the youngest such flood lava event on Mars, the eruption occurring about 600 million years ago and in just a matter of a few weeks — because lava is thought to flow much faster in Mars’ weak gravity — poured out enough material to cover an area about the size of Great Britain.
Today’s picture is near the head of Athabasca, where the hardened lava flow is thinnest. Thus, it did not bury the crater, but merely rushed past, possibly as it did so contributing to the erosion that left this crater upraised.