Tag: geology

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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, was taken on July 17, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the scientists label as an alluvial fan.

I have also seen them label this kind of avalanche as mass wasting, where the material moves down slope suddenly in a single mass.

The image shows the aftermath of such an event, after a large blob of material broke free from the mountainside and slid almost as a unit downhill to settle more than two miles away on the floor of the canyon. The distance traveled and the blobby nature of the flow both reveal how the lower Martian gravity changes the nature of such events, compared to what you might see on Earth. The flows can travel farther, and can hold together as a unit easier.

The overview map below not only provides the context, but it tells us that such events are remarkably common in this place.
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On Mars, one of the most common kinds of landscape is called chaos terrain. Made up of mesas, buttes, and cross-cutting random canyons, this geology is not seen on Earth, and when first identified by scientists in early orbital pictures in the 1970s, it baffled them. While it is clear that some form of erosion process caused it, the scientists did not have enough data then to figure out what that process was.

Today scientists have a rough theory, based on what they now know about Mars’ overall geology and its climate and orbital history. The canyons of chaos terrain were originally fault lines where either water or ice could seep through and widen. See this January 2020 post for a more detailed explanation.

Most of the cool images I have posted of chaos terrain have been in places in the mid-latitudes that are covered with glaciers. See for example this December 2019 post of one particular mesa in glacier country, with numerous glaciers flowing down its slopes on all sides. That mesa is quite typical of all such mesas in the mid-latitudes.

Today’s cool image above, cropped to post here, takes us instead to the Martian very dry equatorial regions. The photo was taken on May 17, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and like mid-latitude chaos, it shows a collection of random mesas with canyons cut almost randomly between.

Unlike the mid-latitudes, however, there is no evidence of glaciers here. Instead, the canyons and mesa slopes are covered with dust, shaped into wind-blown dunes.

As always, the overview map below gives us some context.
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Today’s cool image is also today’s picture of the day from the science team of the high resolution camera on Mars Reconnaissance Orbiter (MRO. That picture, rotated, cropped, and reduced to post here, can be seen to the right. As the caption authors Sharon Wilson and Sarah Sutton write:

The smooth volcanic surfaces in the Gordii Fossae region are sometimes interrupted by long, narrow troughs, or fissures. These fissures form when underground faults, possibly involving magma movement, reach the near-surface, allowing material to collapse into pits or an elongated trough. This fissure appears to have erupted material that flowed onto the surface.

If you use your imagination, this trough resembles a gecko with its long tail and web-shaped feet!

This impression is even more evident in the wider image taken by MRO’s context camera below.
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Cool image time! The photo to the right, cropped and reduced to post here, was taken on May 30, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the dusty dry floor of the chaos region of rough terrain in a side canyon of Valles Marineris, near its outlet. The color strip and the bright outcrops suggest that this terrain contains interesting minerals and resources. To determine exactly what those materials are however requires more information not available in this photo.

This ancient chaos terrain is the leftover eroded sea floor of a intermittent inland sea, leftover water from the catastrophic floods that are theorized to have flowed out of Valles Marineris and carved its gigantic canyons.

The overview map below shows this hypothesized sea.
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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, was taken on August 29, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the scientists label an “inverted channel in Arabia Terra,” a small example of the more than 10,000 miles of fossilized rivers in this region on Mars that scientists have identified using MRO.

They are made of sand and gravel deposited by a river and when the river becomes dry, the channels are left upstanding as the surrounding material erodes. On Earth, inverted channels often occur in dry, desert environments like Oman, Egypt, or Utah, where erosion rates are low – in most other environments, the channels are worn away before they can become inverted. “The networks of inverted channels in Arabia Terra are about 30m high and up to 1–2km wide, so we think they are probably the remains of giant rivers that flowed billions of years ago. [emphasis mine]

Since this fossilized river is located at 11 degrees north latitude, smack in the middle of the dry equatorial regions of Mars, it has certainly been a dry desert for a very long time. You can see how barren the terrain appears by looking at the wider view afforded by MRO’s context camera below.
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Cool image time! The photo to the right, cropped, reduced and annotated to post here, was taken on July 30, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The left image shows a pit that the scientists label a “vent” near the giant volcano Pavonis Mons. The right image is identical, except that I have brightened it considerably to bring out the details in the shadowed area.

As you can see, this pit is filled, and does not appear to have any existing openings into more extensive underground passages.

The white dot on the overview map on the right shows this vent’s location, to the south of Pavonis Mons, and in line with the giant crack that splits three of Mars’ four largest volcanoes. The vent is even aligned the same as that crack, from the northeast to the southwest. The black dots mark the locations of the many cave pits found in this region.

Was this a volcanic vent? If you look at the full image you will see that this pit aligns with a shallower pit to the southwest, with a depression linking the two. Visually this suggests this is a faultline which in turn makes for a good outlet point for lava flow.

Though the data suggests this is a volcanic vent, that supposition is as yet unproven. The full image does not show much evidence of a flow from the pit, which suggests instead that we are merely looking at a spot where the ground cracked along fault lines.

Today’s cool image is another example of scientists finding cool things hidden within distant pictures. The small white rectangle on the overview map to the right shows us where we are heading, to the severely eroded lava plains to the southwest of Mars’ largest volcano, Olympus Mons.

The white spot is about 500 miles from the caldera of Olympus Mons. In elevation it sits about 58,000 feet below that caldera, more than twice the height of Mt. Everest. Yet, despite these great distances, the material at that white rectangle was almost certainly laid down during an eruption from Olympus Mons, thus illustrating the gigantic scale of volcanic events on Mars. Because of the red planet’s light gravity, about 38% of Earth’s, not only can lava flow farther, it does so much faster.

The second image below is a wide angle photo taken by the context camera on Mars Reconnaissance Orbiter (MRO) in January, 2012, rotated, cropped, expanded, and enhanced to post here.
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Cool image time! The photo to the right, cropped and reduced to post here, was taken on July 2, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It provides us just one more clear example of the many glaciers found in that 2,000-mile-long strip of chaos terrain at 30 to 47 degrees north latitude that runs between the northern lowland plains and the southern cratered highlands, a region I like to call Mars’ glacier country.

What makes this glacial feature interesting is that these ice-filled alcoves are south-facing, which in the northern hemisphere means they get the most sunlight. Yet, the ice here remains, well-protected by its layer of dust and debris. Think of the dirty ice slush that manages to survive the longest on city streets in the spring. The dirt acts as protection so that the ice takes more time to melt.

The overview map as always provides our context.
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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, shows one small section of a 30-mile-wide unnamed crater in the cratered equatorial regions of Mars northeast of Hellas Basin. Taken on July 21, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), the science team labeled merely as “Rocky crater fill.”

Being at 17 degrees south latitude, there shouldn’t be any ice features in this crater, and the high resolution image to the right seems to confirm this. All we see is an endless plain made up of innumerable small sharp rock ridges interspersed with small low areas filled with sand dunes. This is bed rock, and if its strange stucco-like appearance was caused by a past glacial era, that era is long gone.

Below is a mosaic showing the entire crater, created from two MRO context camera images.
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Cool image time! The photo to the right, rotated, cropped, reduced, and enhanced to post here, was taken on June 7, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The left image shows what the scientists have dubbed a “lozenge-shaped depression” in the middle of an unnamed 60-mile-wide crater in the southern cratered highlands of Mars. The right image shows the same exact depression, but I have brightened the photo in order to see the details in the shadowed depression.

Though the image is inconclusive, the bottom of the darkest spot in that depression cannot be seen, suggesting it could be an entrance into a larger void below.

Even if there is no voids below, why is this depression here? What caused it? The wider view of MRO’s context camera below might give us a hint.
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Today’s cool image provides a nice illustration why scientists have long assumed that in the distance past there had been catastrophic floods of liquid water on Mars. The photo to the right, rotated, cropped, and reduced to post here, was taken on July 6, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows an east-west gully cutting between mesas to the north and south.

Because the highest mesas seem to be aligned, this suggests they were once part of the same formation, and something came along to carve that gap and gully between them.

What made the break? The overview map below as usual provides some context, which also provides a possible explanation.
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