Tutorial
Mass Movement
Mass movement features are related to the transport of rock, sediment, or mud down a slope. Examples on Earth include landslides and avalanches. Scientists have observed many mass movement features on Mars, and scientists have even witnessed some events occurring on Mars today! This shows that mass movement is currently an active geologic process on the Red Planet.
Mass movement events can sometimes be triggered by seismic or water activity—on Earth, some examples of triggers are earthquakes and heavy rainstorms. The potential for the involvement of liquid water is especially exciting for planetary scientists, as liquid water is necessary for life as we know it to occur. While it doesn’t rain on Mars today, small amounts of water released from the subsurface may be involved in certain types of mass movements in the present day. Water was likely much more of a factor for triggering mass movements in Mars’ past. It is unknown whether Mars has earthquakes—the Insight lander in 2016 will investigate this—but seismic activity from meteorite impacts may also trigger mass movement activity.
Landslides
Landslides occur when large volumes of dirt or rock slip down a slope or cliff face. They consist of an alcove where the material that fell down the slope came from, and a fan at the base of the slope where the material was deposited. There are many different types of landslides, defined by a number of factors such as water content, how the slide starts, and how it moves downslope.
Practice identifying landslides
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Landslide in Shalbatana Vallis
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Tongue in the Hellas basin
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Delta in Jezero Crater
Yes, this is a landslide!
The apron of this large landslide has spread out nearly 2.5 km across the floor of a Martian valley!
This is a glacial tongue.
Notice the shape of the feature and the lines suggesting that it has flowed downhill. The ridges around the edges of the tongue resemble glacial moraines—debris that has accumulated along the margins of a flowing glacier as it moves.
This is a delta.
This is indeed a fan of material, but it was deposited at the mouth of a river where it entered a crater as opposed to the base of a slope from a landslide.
Gullies
Gullies typically consist of three parts: An alcove at the top of the slope (a hollow created by the movement of material downslope), a channel in the middle, and a fan at the base where the material that fell from the alcove is deposited. Landslides can occur within gully channels, and certain types of landslides (such as “debris flows”) can form gullies themselves. They commonly occur on slopes such as crater or valley walls, and are only found at latitudes higher than about 30° in either hemisphere.
Practice identifying gullies
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Tongue in Martian fretted terrain
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Gullies in a crater wall
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Landslides in light-toned layered material in Valles Marineris
This is a glacial tongue.
This feature has a fan, but it sits within an alcove (there is no alcove in the tongue) and has no carved channel, so it is not a gully. It also exhibits flow lines, which are not seen in gullies.
Yes, these are gullies!
These gullies in the wall of a southern hemisphere crater on Mars have a typical alcove-channel-fan morphology.
These are landslides.
These features have alcoves and aprons—features of every landslide—but they lack incised (carved into the rock) channels, which are a defining characteristic of gullies.
Slope Streaks
Slope streaks are dark lines found on slopes in dusty areas on Mars. They are smooth and relatively flat. Scientists tend to think that slope streaks are small dust avalanches, where the fine-grained light-toned dust that blankets much of Mars has slid away to reveal the darker surface underneath. Over time, dust accumulates over the streaks and causes them to lighten, making them "appear" and "disappear" in satellite images.
Practice identifying slope streaks
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Tongue in Martian fretted terrain
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Gullies in a crater wall
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Landslides in light-toned layered material in Valles Marineris
These are gullies.
While these features appear somewhat dark, the dark material is sitting within channels of gullies. These features also have significant relief, whereas slope streaks are relatively flat.
TThese are dust devil tracks.
The dark lines here are on a flat plain rather than a slope. They mark the paths of dust devils swirling across the landscape, removing fine-grained dust from the surface to reveal the underlying darker rock.
Yes, these are slope streaks!
These dark slope streaks are located on the wall of a crater. Their shape is very similar to that of fine powdery snow avalanches on Earth, but on Mars these are avalanches of fine-grained dust.
Boulder Tracks
Boulder tracks are lines of pits formed when a boulder falls down a slope, such as a crater wall. The tracks end where the boulder stopped moving. Thanks high-resolution satellite images from orbiters at Mars, we can actually see these boulders! The movement of these boulders may be triggered by factors such as gravity or meteorite impacts.
Practice identifying boulder tracks
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Tongue in Martian fretted terrain
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Gullies in a crater wall
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Landslides in light-toned layered material in Valles Marineris
Yes, these are boulder tracks!
Each of the dark lines here is an individual boulder track. You can see that many boulders have fallen down this slope! Some are solid lines, suggesting the boulders rolled or slid downhill, while others are a line of dots, which suggests the boulders bounced down the slope.
These are slope streaks.
Some of the thinner dark streaks here might resemble boulder tracks at first glance, but the majority of them are much wider than boulder tracks, some with triangular shapes.
These are landslides.
Look closely—can you see the light-toned (white in this image) material in the layers near the top of this crater wall? Material is falling off (eroding) of these layers and moving down the slope of the crater wall, forming aprons of material lighter than the surrounding wall.