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The steep sudden foothill of Olympus Mons

Olympus Mons on Mars

Today’s cool image starts from afar and zooms inward. The elevation map to the right shows Olympus Mons, the largest volcano on Mars and in fact the entire solar system. About 600 miles across, from the edge to its peak this volcano rises about 54,000 feet, with an actual height relative to Mars’ “sea level” of just under 70,000 feet, more than twice as high as Mount Everest on Earth.

The cross-section of this volcano is so large it would cover almost all of France if placed on Earth. As a shield volcano, it was formed by many many volcano flows that laid down many layers of lava, with some in its northwest quadrant thought to be as recent as 2 to 115 million years ago.

Our cool image today is located at the white rectangle at the southeast edge of this volcano, and illustrates how those many lava flows could create such a large shield volcano with such a large cross section.

Mosaic of two MRO context camera photos
For full images go here and here.

High resolution view  of lava flows
Click for full image.

The first image to the right is a mosaic made from two context photos taken by Mars Reconnaissance Orbiter (MRO). Rotated to post here, it shows that sharp and very steep sudden edge of this giant volcano. If you look close on the plateau you can see what look like numerous flow lines going downhill to the south, all evidence of a past lava flow.

The white outline marks the location of the second photo, taken on March 4, 2021 by the high resolution camera on MRO and rotated, cropped, and reduced to post here. This image shows in close-up those flow lines as they draped themselves around higher ridges as they streamed downward.

The question that we Earthlings ask when we look at Olympus Mons is this: How was it possible for the gentle eruption of lava from the volcano’s caldera hundreds of miles away possibly reach the mountain’s edge as seen in these images? Lava on Earth might flow a few miles, even tens of miles, before solidifying. But hundreds of miles? It doesn’t seem possible.

But it is. This is Mars, with about 38% of the gravity of Earth. As I noted in an early post about one amazingly long lava river on Mars (as long as the Columbia River), molten lava on Mars can travel very large distances, and does so very quickly.

What built Olympus Mons was probably many eruptions, each of which was able to lay down very fast — possibly in only a matter of weeks — a new layer of lava that covered the volcano from the caldera to the very edge we see here. The curved flow around that ridgeline shows us the last bits of that fast flow before it finally stopped at the volcano’s steep, sudden, and sharp foothill edge.

Someday we will be able to drill into these layers, and very precisely date every major eruption, mapping out the volcanic history of Mars and how those eruptions affected the planet’s changing climate. Mars’ geological and climate history then will no longer be a puzzle, but an explanation for how one type of planet evolved over time.


Conscious Choice cover

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Conscious Choice: The origins of slavery in America and why it matters today and for our future in outer space, is a riveting page-turning story that documents how slavery slowly became pervasive in the southern British colonies of North America, colonies founded by a people and culture that not only did not allow slavery but in every way were hostile to the practice.  
Conscious Choice does more however. In telling the tragic history of the Virginia colony and the rise of slavery there, Zimmerman lays out the proper path for creating healthy societies in places like the Moon and Mars.


“Zimmerman’s ground-breaking history provides every future generation the basic framework for establishing new societies on other worlds. We would be wise to heed what he says.” —Robert Zubrin, founder of founder of the Mars Society.


All editions are available at Amazon, Barnes & Noble, and all book vendors, with the ebook priced at $5.99 before discount. The ebook can also be purchased direct from my ebook publisher, ebookit, in which case you don't support the big tech companies and I get a bigger cut much sooner.


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  • Curious if the volcano started when there was liquid water on Mars. The escarpments at the base look very similar to volcanic islands on Earth.

  • Jeff Wright

    Alba Mons is larger but not as tall-but as part of the Tharsis rise it beats Tamu Massif. I would love to see it made perfectly circular. Mayon is my favorite.

  • Lee Stevenson

    This bloody huge volcano has fascinated me my whole life. I am not surprised that there has been (relatively) recent activity. If there is still a core of magma inside, it has a helluva lot of insulation! Take a look at this stunning 2004 image of the caldera… I count at least 6 extant remains of caldera events, the top right having almost 0 craters worth talking about, meaning it must be (relatively) young. It’s the crater to the top that intrigues me the most, Bob, you can answer this question, crater or caldera? I’m suspecting the latter, but not so sure….

  • Lee Stevenson

    You have to download the image to see the top crater…. Sorry, I should have mentioned… It is well worth it!!

  • Jeff Wright

    A caldera results from collapse…though it is called “Crater Lake” that is the caldera left behind by Mount Mazama. St Helens didn’t blow its guts out-rather, the bulge went beyond the angle of repose-and a long run-out landslide unpopped the flank eruption/pyroclastic flow on top of that. Galeras hurt Stanley Williams and Nevad del Ruiz hit Armero with a lahar. Maars look like impact craters. Maar is a shallow crater. Paricutin..though a not considered a separate volcano. Vulcanologist and seismologists are communicating better these days at least.

  • Max

    I see six? large impact craters near the summit.

    On your link I see a caldera that has collapsed in on itself. Straight clean cracks, flat surface, the upper one tilting downward. I’m thinking the hollow place under the center is probably miles in diameter.

    The upper part of Mount Olympus is in a near vacuum… In space. Even in low gravity, the pressure to push a river of fluid that high must have been extreme. Any Crack that would open up in the volcanoes side would see a high pressure torrent pouring through it, dropping the lake of lava at the top suddenly.

    I agree with Blair, The only explanation for the high cliffs around the base is if there was water to solidify the lava. (or “ice”… glaciers sliding off the mountain, miles high natural retention dam to hold in the melt water like a moat the size of France) The only other possibility is core pressure uplift on the volcano which is unlikely due to its massive size.

    The author of ringworld fantasized of a large underground cavern inside mount Olympus with a flat floor of solidified lava. A big enough space when pressurized to fly airplanes inside.

  • Max: You are treading on dangerous scientific ground when you say these words: “The only explanation for [anything].” It is far too soon to come to such a conclusion so certainly, especially with what little we know.

  • Max

    You are right, I know better and should proofread what I write.
    perhaps it should’ve said “the only explanation I could think of” (only I didn’t think of it, Blair did). (Unexpected rain showers has slowed down speed today so I am able to read and write comments while I’m driving)

    This reminded me of an earlier conversation on the same subject and no better plausible explanation has arisen yet. I do love a scientific mystery…

    Speaking of scientific certainty’s… I was listening earlier to an author talking about his new book on the case for permanently removing farm animals (cows) to save the planet from natural gas (methane) and to use the farmland for crops for just humans.
    Like my poor wordage, he thinks “The science is settled”, becoming vegan is the only hope that this planet has… what an incredible lack of critical thinking, accepting the propaganda of the worlds overlords for what is pure “science fiction” not actual science. I could counter every “factual statement” that he made with the laws of nature, math and logic that he is violating.
    The biggest one that applies to all so called greenhouse gases;
    Second law of thermal dynamics!
    Heat flows from the hotter object to the cooler one, no cold greenhouse gas can radiate heat to a warmer planet surface, the surface which is hotter only radiate heat towards the colder. (climb into the carbon dioxide / dry ice freezer at your local grocery store to get warm if you don’t believe me)

    Cows mostly eat hay and grass which humans do not eat, for the most part, we do not compete for the same food substance (we use grains to “fatten up” cows… and humans) can you imagine how much of the world we could feed with our corn instead of turning it into ethanol? we spend more energy in a three step process to make corn into alcohol for cars, then the power that alcohol produces burning in those cars. (at 100 proof, the alcohol is half water “reducing” gas mileage)

    Cows are most often pastured on land that is not suitable for farming, creating meat, milk, cheese for human consumption in a near perfect symbiotic relationship.
    Do cows make methane? NO!
    Only anaerobic bacteria, responsible for rot, has the Biology for making methane. Is there any carbon-based life forms on this planet that “doesn’t rot” and turn into methane when it dies?

    The point is, if the cows did not eat the hay and grass, the plants go to waste and will freeze and rot under the snow come winter, just like the tree leaves, and turn into methane anyway! Removing all the animals will gain nothing!

    Life has covered this planet for more than a billion years, have you ever asked yourself why after all that time there is only 1.8 ppm measurable methane? (1.8 ppm is the same as $1.80 out of a million dollars) more rare than helium which is measured at 4 ppm which floats right out into space. It is as close to zero as any plentiful gas can get. So when they say that it’s 14 times more dangerous than carbon dioxide… what is 14×0? Yep zero! That’s because methane oxidizes when it comes in contact with oxygen… The gas company has accurate measurements if you call them.
    What is the source of earth’s methane? Bacteria eating dead stuff is one, (not the permafrost because most bacteria doesn’t survive the freezing process)
    Fossil fuels from continental drift passing over ancient seabed/ calcium carbonate lime stone is another. (natural gas)
    The largest source of methane is an active sun which will throw billions of tons of hydrogenated gases into our atmosphere from a coronal mass ejection. An X class flare will light up the sky for thousands of miles, volatile gases burning creating water, nitrogen, carbon dioxide ect. as our magnetic field draws it in. You can tell what the substance is by the color it burns.

    Thanks, I just had to get that off my chest. I feel better now.

  • Lee Stevenson

    @Max, I meant that the caldera shows evidence of 6 eruptions, and following “settlings”, count the radius’s.. ( radei?)…. I’m more interested in the singular crater/caldera higher up on the picture.
    Regarding the slightly off topic rant regarding methane from cows, (I like off topic!), I don’t know enough to state any facts regarding the contribution of cows to global warming, but I know enough about thermodynamics to know that heat will flow from warm to cold via convection and conduction, but the problem with “greenhouse gases” is that heat gets reflected by those gases, there is no, ( or very little) transfer of heat, it is just reflected back down.

    I do actually believe that the world is not big enough to allow us all to eat steak, and I hope that “vat” produced meat becomes reality, because I like a nice steak. I also think that saying cows live on land which would otherwise be a carbon producer is a bit of a lame ( shoot it! It’s lame!) argument, food crops are grown on some of the worst soil in the world, with the aid of fertilizer, which runs off into the water systems and destroys the nitrogen cycle, releasing CO2……. Oh sod it…. I’ll take mine medium with the fries please!

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