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Cool image time! The photo to the right, cropped and reduced to post here, was taken on June 29, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). In this one spot we see three obvious volcanic features, all however formed by different processes.
The location of this image is west of Olympus Mons. It sits on the vast lava plain that was laid down by that volcano, the largest in the solar system.
In order of likely occurrence, the cone probably came first. It likely indicates a past eruption coming up from below to create a small volcano.
The shallow meandering channel that sweeps around it to the north and east probably marks a later lava flow coming down from Olympus Mons.
The deeper straight fissure to the south probably came last. It is a graben, a crack caused by the uplift of the entire surface because of pressure from a magma chamber below, causing cracks to form as the surface is stretched.
Three different volcanic events, each probably taking thousands of years, with maybe thousands to millions of years between them. The context map below adds weight to the scale of time and size represented by this one Martian photo.
This image is sitting close to what scientists have defined as the “sea level” of Mars, or zero elevation. The caldera of Olympus Mons, sits at about 70,000 feet, or more than thirteen miles higher, and more than twice as high as Mount Everest. Moreover, that peak is about 200 to 250 miles away, with the volcano’s first foothills more than 100 miles to the west.
Yet, even at that distance and height, the volcanic eruptions of Olympus Mons and gigantic magma chamber below it helped shape this place, and it did it over a very long time span across a number of distinct volcanic events.
This is volcanism at a scale that is alien to anything so far studied on Earth. It will take a lot of in situ research to untangle it and gain even a superficial understanding of it. Right now we only know that it happened.