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Geomorphological evidence for a dry dust avalanche origin of slope streaks on Mars


Mars has several different types of slope feature that resemble aqueous flows. However, the current cold, dry conditions are inimical to liquid water, resulting in uncertainty about its role in modern surface processes. Dark slope streaks were among the first distinctive young slope features to be identified on Mars and the first with activity seen in orbital images. They form markings on steep slopes that can persist for decades, and the role of water in their formation remains a matter of debate. Here I analyse the geomorphic features of new slope streaks using high-resolution orbital images. Comparison of images before and after streak formation reveal how this process affects the surface and provides information about the cause. These observations demonstrate that slope streaks erode and deposit material in some instances. They also reveal that streaks can jump slopes and may be erosive very near their termini. These observations support a formation model where dark slope streaks form as ground-hugging, low-density avalanches of dry surface dust. Such streaks need not be treated as Special Regions for planetary protection.

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Fig. 1: Formation of ridges corresponding to lobe boundaries within a new slope streak.
Fig. 2: Evidence for erosion near slope streak termini.
Fig. 3: Slope streak topographic interactions.
Fig. 4: Interactions between new and existing slope streaks.

Data availability

All of the data used in this study are available via the NASA Planetary Data System and/or the HiRISE team website at Supplementary Table 1 provides the geographic locations of all images used.


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This work was funded by the NASA Mars Data Analysis Program under agreement number 80HQTR17T0022. HiRISE data were collected, processed and released by NASA/JPL/University of Arizona and the MRO project.

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Correspondence to Colin M. Dundas.

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Extended data

Extended Data Fig. 1 Slope streaks fading rapidly and forming in concentrated bursts.

From a to b, the slopes were reset in less than one Mars year: virtually all existing streaks faded and were replaced by a large number of new streaks. From b to c, a handful of new streaks formed while the existing streaks remained distinct, possibly fading slowly, over nearly three Mars years. This demonstrates that the rapid fading and intense streak formation from a to b is not a characteristic of this site at all times, and instead indicates a fading/obliteration event and subsequent burst of streak formation, followed by reversion to a slower background rate of change.

Extended Data Fig. 2 Anaglyph demonstrating topographic control of a dark slope streak.

Downhill is to the right. The streak was interrupted by a ridge, which is likely 1-2 meters high based on the wavelength47. The flow proceeded obliquely downhill along the ridge until overtopping it at several local lows. This behavior is not expected for gradual seepage.

Extended Data Fig. 3 New slope streak straddling the edge of an old avalanche scar.

The shaded scar margin visible in a is along the median axis of the streak in b. This demonstrates that streaks need not remove the entire failure-prone layer. Additionally, while they can be controlled and deflected by subtle topography, the flow was capable of proceeding on both the high and low sides of the scarp with no effect on its behavior, indicating that it was a superficial phenomenon. Downhill is to the lower right.

Extended Data Fig. 4 Example of mass movement in a new slope streak.

Scarps and shading from lumpy dust deposits are visible in a, but an additional scarp with no corresponding feature is present in the new scarp in b (arrow), demonstrating movement of a thick body of dust. Also note numerous small patches within the streak that were unaffected by its passage. Downhill is to the left.

Extended Data Fig. 5 Example of mass movement in a new slope streak.

a is from before the streak formed, while b and c are after. Changes in topography are distributed throughout the streak and along the southern margin; arrows indicate particularly distinct examples such as pits or reshaping of surface features. Downhill is to the right.

Extended Data Fig. 6 Additional evidence for incision extending to near slope streak termini.

The ridges in the western part of panel a have narrow incised channels in the troughs between them, similar to Fig. 2. Panel b shows detail. This erosion stops at approximately the red dotted line, which is also the approximate distal limit for slope streaks at this site.

Extended Data Fig. 7 Example of a spire streak from Pavonis Mons.

The surface is generally flat, but the streak was capable of running up and over obstacles. The edges of the streak appear sharp at low resolution (a) but are jagged in detail (b), likely due to interactions between the wind and regular, subtle surface relief.

Supplementary information

Supplementary Information

Supplementary Table 3 and descriptive information for Data 1 and 2.

Supplementary Data 1

List of sites and coordinates; see Supplementary Information for details.

Supplementary Data 2

List of new slope streaks documented in this work; see Supplementary Information for details.

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Dundas, C.M. Geomorphological evidence for a dry dust avalanche origin of slope streaks on Mars. Nat. Geosci. 13, 473–476 (2020).

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