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Martian Landslides

Martian Landslides. THE RHEOLOGICAL DEBATE. Summer Brown 03/22/06. BRIEF DESCRIPTION OF MARS. SIX PROCESSES THAT ARE CURRENTLY HAPPENING OR HAVE HAPPENED IN THE PAST ON MARS:. Cratering Tectonics Aeolian Hydro Landslides Volcanic. University of Illinois. TIMELINE. Noachian.

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Martian Landslides

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  1. Martian Landslides THE RHEOLOGICALDEBATE Summer Brown03/22/06

  2. BRIEF DESCRIPTION OF MARS

  3. SIX PROCESSES THAT ARE CURRENTLY HAPPENING OR HAVE HAPPENED IN THE PAST ON MARS: • Cratering • Tectonics • Aeolian • Hydro • Landslides • Volcanic University of Illinois

  4. TIMELINE Noachian Hesperian Amazonian -3500 -3000 -2500 -2000 -1500 -1000 -500 0 The three broad epochs are defined by the number of impact craters on the surface. WikipediaFree Encyclopedia

  5. University of Illinois

  6. VALLES MARINERIS IS THE MOST NOTICEABLE SURFACE FEATURE OF MARS Vast system of interconnected canyons near the equatorEntire canyon is 4500 km long (almost width of U.S.)Can be as much as 7 km deep! (Grand Canyon is ~1.2) University of Illinois

  7. INTRO TO LANDSLIDES ON MARS

  8. Resemble terrestrial landslides to a high degree. • Occur mainly in the Valles Marineris canyon system. Harrison and Grimm, 2003

  9. Typically a few tens of kilometers wide and recede a few kilometers into wall. • Volume can range from tens to thousands of cubic kilometers. Harrison and Grimm, 2003

  10. Landslides are the most recent geomorphological process to occur on Mars. • They are sparsely cratered (suggesting late Hesperian to Amazonian) Harrison and Grimm, 2003

  11. Some indication of faulting postdating the landslides. • Slides have longitudinal grooves, rather than transverse ridges like their terrestrial counterparts. Harrison and Grimm, 2003

  12. Credit: NASA/JPL/Arizona State University

  13. WHAT CAN BE LEARNED BY STUDYING LANDSLIDES ON MARS?

  14. Once we can constrain the morphology and geometry, modeling can be used to determine rheologies, giving implications for conditions in which the landslides occurred (i.e. existence of liquid water near the surface during the late Hesperian and Amazonian)

  15. THREE STUDIES: • Rheological constraints on martian landslides (Harrison and Grimm, 2003) • Comparing run-out efficiency of fluidized ejecta on mars with terrestrial and martian mass movements (Barnouin-Jha and Bologa, 2003) • Martian landslides in Valles Marineris: Wet or dry? (Soukhovitskaya and Manga, 2005)

  16. RHEOLOGICAL CONSTRAINTS ON MARTIAN LANDSLIDES Harrison and Grimm, 2003

  17. Harrison and Grimm study landslides in the Valles Marineris using a dynamic finite-difference model and three different modal rheologies (and combinations thereof): • Frictional • Bingham • Power Law

  18. FRICTIONAL Basal resistance is proportional to the normal stress it exerts on the run-out path. The frictional law used in the dynamic model is such that “a change in friction angle will have the same effect as a corresponding change in pore fluid pressure”.

  19. BINGHAM Uses a Newtonian fluid with a finite yield strength. Yield strength in turn causes a solid cap riding on top of flow, which thickens as slide continues over run-out path. Eventually, solid cap consumes entire flow, and slide stops. Higher yield strengths therefore have shorter run-outs.

  20. POWER LAW Can be used when most of the lateral shear is in a thin basal layer. Water content is implicit! A n value of 0 is indicative of a rigid block while a value of 1 represents a Bingham fluid. shear stress, τ = τo + μ(dv/dz)nz is depth, μ is “apparent” viscosity (having no units), and n is a unitless index.

  21. GENERAL AND ACOUSTIC FLUIDIZATION … are combinations of frictional and power law rheologies. For general fluidization, the slide is frictional at failure, but becomes fluidized. Acoustic fluidization, a more specialized version of general, can occur without liquid or gas present. Acoustic waves are transmitted elastically through slide materials, decreasing overburden pressure for short periods, therefore reducing basal resistance.

  22. HARRISON AND GRIMM LOOK AT NINE DIFFERENT LANDSLIDES: 1. California Blackhawk 2. Ophir Chasma3. Ophir Chasma4. Gangis Chasma5. Gangis Chasma6. Coprates Chasma7. Ophir/Melas Chasma 8. Olympus Mons9. Apollo 17 landing site

  23. Credit: NASA/JPL/Arizona State University

  24. Volume was estimated for martian slides using Mars Orbiter Laser Altimeter (MOLA) elevation data from Mars Global Surveyor (MGS) and Viking images for deposit boundary location. Assuming a horizontal base, elevation was inferred from surrounding topography.

  25. Initial conditions were calculated taking into consideration scar width W, scar slope α1, and typical nearby wall slope α2 .

  26. EXAMPLE MODEL RESULTS

  27. RESULTS The general fluidization rheology is the best fit for two of the slides (3 & 4) and arguably best for three (1, 2, & 7). For slides 6 and 8, none of the rheologies produce good fits. This is attributed to a non-landslide origin. Slide 9 is best explained by acoustic fluidization. For slide 5, the Bingham rheology seems to be the best, however, the slide path in longitudinally confined.

  28. CONCLUSION • Frictional rheology tends to produce models which can explain the long run-out landslides • Bingham rheology fails to produce the correct tail shape in the models, even when resolution is increased. • General fluidization consistently seems to be the most reasonable.

  29. FOUR SCENARIOS FOR LUBRICATION OF FORMATIONS • Substantial parts could have been saturated with ice at failure, though energy produced by friction is likely insufficient to melt the ice. • 2. Water may have been present in the liquid phase prior to failure. Perhaps the water table was only a few hundred meters deep. • If lakes existed in the Valles Marineris, water may have infiltrated into the walls, providing sufficient pore pressure for later landslide fluidization. • In the absence of water, CO2 may have been a suitable fluidizing agent. Depressurization of subsurface CO2 liquid causes it to flash into the gaseous phase and mix broken landslide material into a turbulent cloud of dust, rocks, ice, and gas.

  30. COMPARING RUN-OUT EFFICIENCY OF FLUIDIZED EJECTA ON MARS WITH TERRESTRIAL AND MARTIAN MASS MOVEMENTS. Barnouin-Jha and Baloga, 2003

  31. This study uses the concept of run-out efficiency to characterize fluidized ejecta rheology on Mars. Run-out efficiency is obtained by balancing the kinetic energy of the ejecta and the total work lost during its deposition.

  32. For ejecta, the run-out efficiency is 1/R, where R is the resistance coefficient. For mass movement of debris, the run-out efficiency is L/H, where L is the run-out distance and H is the onset height. 1/R = L/H

  33. In order to compare run-out efficiencies of fluidized ejecta with those of landslides, necessary measurements are: run-out distance, rim-to-rim diameter, volume of the ejecta flows, and H (in the case of landslides).

  34. DATA SOURCES Data used is from several fresh craters in a volcanic plain and landslides in Coprates and Ganges Chasm. Obtained from DTMs of MOLA and imagery from Viking orbiter.

  35. Preliminary results for run-out efficiency versus flow volume of Martian fluidized ejecta and landslides, and a few terrestrial mass movements.

  36. RESULTS (as applicable to landslides) Run-out efficiencies of the observed landslides are low relative to the other data sets. They still fall within a broader set of data for terrestrial and extraterrestrial mass movements.

  37. IMPLICATIONS This all indicates that gravity is not the primary cause for the differences… giving implications that the martian landslides formed in a environment drier than that of the ejecta from the volcanic field.

  38. SO WHICH IS IT??? WET OR DRY

  39. MARTIAN LANDSLIDES IN VALLES MARINERIS: WET OR DRY? Soukhovitskaya and Manga, 2005

  40. The objective of this study was to determine whether the landslides in Valles Marineris really were wet or dry and constrain water availability at the time the landslides occurred. This is done in three steps:

  41. 1. COMPARING THE POWER-LAW RELATIONSHIP BETWEEN VOLUME AND RUNOUT DISTANCES FOR EARTH AND MARS 2. COMPARING OBSERVATIONAL DATA ON EARTH WITH MODELS FOR DRY AND DILUTE FLOWS 3. ESTABLISHING A CONSISTENT RUNOUT DISTANCE-GRAVITY SCALING LAW FOR DRY LANDSLIDES

  42. 1. COMPARING THE POWER-LAW RELATIONSHIP BETWEEN VOLUME AND RUNOUT DISTANCES FOR EARTH AND MARS 2. COMPARING OBSERVATIONAL DATA ON EARTH WITH MODELS FOR DRY AND DILUTE FLOWS 3. ESTABLISHING A CONSISTENT RUNOUT DISTANCE-GRAVITY SCALING LAW FOR DRY LANDSLIDES

  43. 1. COMPARING THE POWER-LAW RELATIONSHIP BETWEEN VOLUME AND RUNOUT DISTANCES FOR EARTH AND MARS 2. COMPARING OBSERVATIONAL DATA ON EARTH WITH MODELS FOR DRY AND DILUTE FLOWS 3. ESTABLISHING A CONSISTENT RUNOUT DISTANCE-GRAVITY SCALING LAW FOR DRY LANDSLIDES

  44. Schematic landslide diagram where L is run-out distance and V is volume.

  45. MODELS FOR THE RELATIONSHIP BETWEEN L, V, AND GRAVITY

  46. DRY GRANULAR FLOWS Kilburn and Sorensen (1998) model based on mechanical energy dissipation, frictional stress, and fragmentation of flow particles: whole body flow L ~ g V1/3basal boundary flow L ~ g5/6 V1/2 Iverson (1997) model for oscillating grains in a dry boundary layer is identical to that for whole body flow.

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