A Mud Flow on Mars?

Post contributed by Prof. Lionel Wilson, Lancaster University, UK and Dr. Peter J. Mouginis-Mark, Hawaii Institute of Geophysics and Planetology, USA.

Image 1 shows a distinctive flow deposit southwest of the Cerberus Fossae on Mars.  The flow source is a ~20 m deep, ~12 x 1.5 km wide depression within a yardang field associated with the Medusae Fossae Formation.  The flow traveled for ~40 km following topographic lows to leave a deposit on average 3-4 km wide and up to 10 m thick.  The surface morphology of the deposit suggests that it was produced by the emplacement of a fluid flowing in a laminar fashion and possessing a finite yield strength. There is an ongoing debate about whether flows in this region of Mars are lava flows or water-rich debris flows.

Image 1: Location of mudflow deposit on Mars.

Image 1: Location of the distinctive flow deposit, called Zephyria Fluctus, just north of the equator on Mars. The inset at top left shows the broader context of the flow. The grey area is the flow’s extent and black boxes indicating the position of Images 2 and 3 (Fig. 2) and Image 4 (Fig. 4). The inferred flow direction is from SW to NE. Mosaic of CTX images D01_027675_1806, D04_028941_1805 and G19_025697_1803.

Topographic data from a digital elevation model (DEM) was used to model the dynamics of the motion and the results imply that the fluid had a Bingham rheology with a plastic viscosity of ~1 Pa s and a yield strength of ~185 Pa.  Although the low viscosity could be consistent with the properties of komatiite-like lava, the combination of values of viscosity and yield strength, together with the surface morphology of the deposit, suggests that this was a mud flow.

Image 2: Close-up view of the source of the flow located in a depression

Image 2: Close-up view of the source of the flow, which created a depression within materials interpreted to be a fine-grained eolian deposit associated with the Medusae Fossae Formation. Boxes at top left and lower right show two of the more interesting aspects of this source area in greater detail. Top left shows a series of overlapping ridges and at lower right some of theHiRISE image ESP_025697_1805.

Image 3: Topography of the source area.

Image 3: Topography of the source area derived from a stereo pair of HiRISE images (ESP_025697_1805 and ESP_037169_1805). The elevations are references to the MOLA Mars datum.

Comparison with published experimental data on sampled mud flow materials implies a solids content close to 60% by volume and a grain size dominated by silt-size particles.  Further, comparison of the ~1.5 km3 deposit volume with the ~0.03 km3 volume of the source depression shown in detail in Images 2 and 3 implies that ~98% of the flow material was derived from depth in the crust.  If this flow deposit is indeed a mud flow, then not only water but also a great deal of fine-grained material was brought up from the aquifer that was its source.

Image 4: Distal portion of the flow, showing textures similar to those in other lavafields on Mars.

Image 4: Distal portion of the Zephyria Fluctus flow, showing textures similar to those in other lava fields on Mars. Part of CTX image D4_028941_1805.

The non-Newtonian properties of such fluid mixtures may have implications for models of the erosion processes in martian channels currently assumed to have been eroded by initially sediment-free water.  The source area of the flow is quite different from volcanic vents seen elsewhere on Mars, raising further questions about the origin of the flow.  Particularly intriguing is the fact that the distal portion of the flow (Image 4) has a surface morphology that is very similar to that of other flows on Mars that are interpreted to be lava flows. This suggests that a reanalysis of certain other flows previously described as lava flows may be in order to investigate if they too are mud flows.

Further Reading

Jaeger, W.L. et al. (2010).  Emplacement of the youngest flood lava on Mars: A short, turbulent story.  Icarus 205: 230 – 243. doi: 10.1016/j.icarus.2009.09.011

Page, D. P. (2010).  Resolving the Elysium controversy: An open invitation to explain the evidence.  Planet. Space Sci. 58: p. 1406 – 1413. doi: 10.1016/j.pss.2010.06.010

Ryan, A. J. and P. R. Christensen (2012).  Coils and polygonal crust in the Athabasca Valles region, Mars, as evidence for a volcanic history.  Science 27: p. 449 – 452. doi: 10.1126/science.1219437

Wilson, L. and P. J. Mouginis-Mark (2014).  Dynamics of a fluid flow on Mars: Lava or mud?  Icarus 233: p. 268 – 280. doi: 10.1016/j.icarus.2014.01.041

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1 Comment

  1. Prof. V.Subramanyan Iyer (Retired)

     /  November 8, 2015

    Excellent images! It looks more like a mudflow rather than a lava flow.

    Reply

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