Date of Graduation

5-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Space & Planetary Sciences (PhD)

Degree Level

Graduate

Department

Space & Planetary Sciences

Advisor/Mentor

John Dixon

Committee Member

Larry Roe

Second Committee Member

Richard Ulrich

Third Committee Member

Kristopher Brye

Fourth Committee Member

Susan Conway

Keywords

Experimental, Gullies, Mars, Mass Wasting, Sublimation

Abstract

Here we present the first set of laboratory experiments under martian atmospheric conditions which demonstrate that the sublimation of CO2 ice from within the sediment body can trigger failure of unconsolidated, regolith slopes, and can measurably alter the landscape. Previous theoretical studies required CO2 slab ice for movements, but we find that only frost is required. Hence, sediment transport by CO2 sublimation could be more widely applicable (in space and time) on Mars than previously thought. This supports recent work suggesting CO2 sublimation could be responsible for recent modification in martian gullies.

A second set of experiments were carried out under martian conditions, investigating the influence of initial slope angle and sediment grain size through on the rate of triggered sediment movement, and on the type of movement (e.g., granular flow or creep). Where the initial study used JSC Mars-1 regolith simulant exclusively, near the angle of repose, these experiments added fine and coarse sand at slope angles down to 10°. We find that the Mars regolith simulant is active down to 17°, the fine sand is only active near the angle of repose and the coarse sand shows negligible movement. Based on our analytical model, motion should be possible at even lower slope angles under martian gravity. We conclude that these mass wasting processes could currently be involved in shaping martian gullies, and intriguingly, CO2-creep process observed in our experiments could provide an alternative explanation for putative solifluction lobes on Mars.

While the sublimation of water ice is a familiar landscape process on Earth, the sublimation of CO2 frost under Mars conditions is not. A comparison of experiments conducted under terrestrial atmospheric conditions with the experiments conducted under martian conditions was performed. We conclude that the rate of pressurization within the pore space of sediment slopes controls both the type and amount of mass wasting triggered. Further, we

propose that the rates of sublimation for water ice under terrestrial conditions are too low to trigger mass wasting, evolving water vapor having ample time to diffuse through the pore space and vent to the atmosphere.

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