Click for original image.

Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on August 24, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

Labeled “flow margin in Elysium Planitia,” it shows the very edge of what scientists believe was the most recent large lava event on Mars, dubbed the Athabasca Valles, that is thought to have occurred only 600 million years ago. In only a matter of weeks the fast flowing lava covered a region about the size of Great Britain. What we see here is the southernmost edge of that flow, with the smooth terrain on the west an older lava flood plain, covered by the new flood lava from Athabasca on the east.

The polygon cracks likely indicate cracks that formed during the hardening process (like the polygon cracks in drying mud). Hot lava then pushed up from below to form the ridges. It is also possible the ridges are what scientists call “wrinkle ridges,” formed when material shrinks during the drying process.

The white dot on the overview map to the right marks the location, with the white rectangle in the inset indicating the area covered by the picture above. That inset, created from a global mosaic of MRO’s context camera images, makes the flow margin very evident, flowing past a small hill and some ridges before ending to the south.

Athabasca might be the youngest known lava flow on Mars, but in this region between the giant Martian volcanoes the surface is covered for thousands of miles with many such flood lavas, each layer signaling a past eruption. Some of that lava came down from the big volcanoes, travelling many many hundreds of miles. Others erupted out of nearer vents, such as Athabasca, which spewed from a point near the western end of the Cerberus Fossae cracks and ran west and south from there.

In all cases the lava flowed fast, because in Mars’ lower gravity it acts more like water.