Tag: avalanches

A weak avalanche season on Mars?

1:39 pm

The north pole scarp
Click for full image.

Today’s cool image from Mars is cool both for what is visible in the photo and for what is not, the latter of which might turn out to be a discovery of importance.

The photo to the right, cropped and reduced to post here, was taken on June 24, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a section of the edge of Mars’ north polar ice cap, with north at the top.

This scarp is probably more than 2,000 feet high, though that height drops to the south as the upper layers disappear one by one from either long term erosion or sublimation. Those layers represent the visible information in the photo that is cool. They give us tantalizing clues about the geological and climatic history of Mars. Each layer probably represents a climate period when the north icecap was growing because the tilt of the planet’s rotation was even less than the 25 degrees it is now. When that tilt is small, as small as 11 degrees, the poles of Mars are very cold, and water ice migrates from the mid-latitudes to the poles, adding thickness to the icecaps. When the tilt grows, to as much as 55 degrees, the mid-latitudes are colder than the poles, and the water ice migrates back to the mid-latitudes.

What is not visible in this picture, however, might be far more significant.
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A Martian avalanche: before and after

6:35 pm

A Martian avalanche: before and after
Click for full resolution animation.

Cool image time! The science team for the high resolution camera of Mars Reconnaissance Orbiter (MRO) today released a beautiful blink animation showing the before and after terrain at an avalanche site along the scarp of Mars’s north pole ice cap.

The animation is very cool, but it is also helpful to align the two images next to each other to carefully study what actually changed. The image to the right, cropped and reduced here, shows both photos. (Thank you to planetary scientist Shane Byrne for splitting the animation for me.). I have added the white bars to indicate the cliff section that broke off during the avalanche. That section was made of water ice, with probably some dust and rocks mixed in, and broke into the blocks that are now scattered on the ground below.

This avalanche itself is actually not unusual and as I noted in an earlier post, is part of an annual season of numerous avalanches that occur on this northern scarp of the polar ice cap each spring. As written by Dr. Candice Hansen of the Planetary Science Institute in Tucson, Arizona,

Every spring the sun shines on the side of the stack of layers at the North Pole of Mars known as the north polar layered deposits. The warmth destabilizes the ice and blocks break loose. When they reach the bottom of the more than 500 meter tall cliff face [about 1,600 feet], the blocks kick up a cloud of dust.

And as Byrne noted to me in an interview when I asked him how it was possible for MRO to image so many avalanches, as they occur,

“It is incredible. I think this is the most incredible thing about the whole process.” said Byrne. “If you fly over a mountain range on the Earth and take a picture, the chances catching an avalanche in progress are almost zero. But on Mars half of the images we take in the right season contain an avalanche. There’s one image that has four avalanches going off simultaneously at different parts of the scarp. There must be hundreds to thousands of these events each day.”

In an email exchange with him today, he also added that this is not the first before and after comparison images obtained. “We’ve been seeing these blockfalls for several years now. That’s partly why these scarps are being so intensively monitored by HiRISE.”

Do these avalanches mean that the Martian northern polar ice cap is shrinking? Maybe, maybe not. Right now scientists think the cap is in a steady state, neither growing or shrinking. These events are thus more likely comparable to the routine calving of ice sections from the foots of glaciers here on Earth, a common tourist destination in the waters of western Alaskan coast.

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Avalanche season at the Martian north pole

3:22 pm

Avalanche on-going at the edge of Mars' north pole icecap
Click for full resolution image.

As the Martian spring started to unfold in April 2019, the focus of many Martian planetary scientists immediately shifted to the northern polar icecap, where they fully expected, based on previous experience, some spectacular events to occur.

I have already reported on this year’s initial observations of the sublimation of the carbon dioxide frost layer. That frost layer, generally less than six feet thick, falls as dry ice snow with the coming of winter, then sublimates away each spring. Since the arrival of Mars Reconnaissance Orbiter (MRO) in 2006 and its discovery of this process by its high resolution camera, these scientists have been monitoring the disappearance of that frost layer from Martian year to Martian year.

That sublimation process also brings with it other spectacular changes, including the coming of frequent avalanches along the high cliff scarps, ranging in heights from 1,500 to 3,000 feet, that comprise the edge of that north pole icecap. The image above, reduced to post here, shows one of the many avalanches found this spring and photographed as they were actually happening. It looks down at the cliff that runs from the left to the lower right of the image, with its top being the flat plateau in the lower left. From the caption, written by Dr. Candice Hansen of the Planetary Science Institute in Tucson, Arizona,

Every spring the sun shines on the side of the stack of layers at the North Pole of Mars known as the north polar layered deposits. The warmth destabilizes the ice and blocks break loose.

When they reach the bottom of the more than 500 meter tall cliff face [about 1,600 feet], the blocks kick up a cloud of dust. (In the cutout, the top layer of the north polar cap is to the lower left.) The layers beneath are different colors and textures depending on the amount of dust mixed with ice.

The linear many-layered look of that cliff face is due to the many layers believed to exist within the permanent water icecap of Mars. To give some perspective, this cliff is several hundred feet taller than the World Trade Center after completion. Those falling blocks are dropping farther than the bodies that horribly fell from the Trade Center the day it was hit by airplanes flown by Islamic terrorists on September 11, 2001.

The map below shows most of the eastern half of that icecap, with the white boxes showing the various places MRO has spotted such avalanches.
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The soft avalanches of Mars

9:23 am

Krupac Crater gullies

Cool image time! The image on the right, reduced in resolution to show here, shows the gullies flowing down Krupac Crater on Mars. Be sure to check out the original, released today by the Mars Reconnaissance Orbiter science team, since they have enhanced the colors to bring out the sandy flows, noting as well that while most of these gullies are found in higher latitudes, this crater at 7.8 latitude has them as well.

Although large gullies (ravines) are concentrated at higher latitudes, there are gullies on steep slopes in equatorial regions. An enhanced-color closeup shows part of the rim and inner slope of Krupac Crater located just 7.8 degrees south of the equator.

The colors of the gully deposits match the colors of the eroded source materials. Krupac is a relatively young impact crater, but exposes ancient bedrock. Krupac Crater also hosts some of the most impressive recurring slope lineae (RSL) on equatorial Mars outside of Valles Marineris.

Below I have cropped out a small section showing, at full resolution, the termination point of one of these flows, indicating where this section is on the larger image to the right. This avalanche is clearly not liquid, though it has a very sandy and soft nature, suggesting — as some scientists have theorized — that liquid from below the surface might have played a part in its flow.

It is important in looking at these images to repeatedly remind yourself that the gravity here is about one third that of Earth, and thus the angle of repose will be different, and that avalanches will behave very differently in this environment. Moreover, Mars’s far colder climate will also effect things. The avalanche we are looking at could not happen in this way on Earth.

close-up of flow

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An avalanche on Mars, as it happens

4:49 pm

Avalanche on Mars

Cool image time! In their routine monitoring for avalanches at the layered deposits at the Martian north pole, the Mars Reconnaissance Orbiter science team captured the avalanche on the right, as it happened.

This picture managed to capture a small avalanche in progress, right in the color strip. … The small white cloud in front of the brick red cliff is likely carbon dioxide frost dislodged from the layers above, caught in the act of cascading down the cliff. It is larger than it looks, more than 20 meters across, and (based on previous examples) it will likely kick up clouds of dust when it hits the ground.

They note that avalanches in this area of Mars are common in the spring when things are warming, and have been documented previously, but possibly not so dramatically.

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Avalanches on Mars

10:28 am

Saturday’s weekly dump of publications from the American Geophysical Union also included a paper that showed visual proof of avalanches on Mars! In this case, the location is Russell Crater, “a large crater in the southern hemisphere that exposes a large dune field in its center.” The avalanches occur because a frost layer made up of dry ice and a little bit of frozen water builds up on the crest of the dunes. When that frost melts, dark streaks about three to six feet wide and about 150 feet long appear, flowing downhill. The scientists believe these are avalanches made up of “a mixing of sand, dust, and unstable CO2 gas.”

wide shot of before and after
Before and after shots of the dark streaks flowing down the dune.

close-up, before and after
Close-ups of the streaks, before and after.

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