Mass Wasting Theme Overview

By Alfred McEwen

Explanation of the theme. “Mass wasting” means rapid downhill movement of rocks and fine particles due to the force is gravity. It includes known active processes on Mars such as rock falls (and/or rolling down hills) and dust avalanches that make dark (and sometimes bright) streaks. Mass wasting also includes larger-scale events that occurred in the past and may occur in the future, but on longer time scales. This can include features ranging in size up to the giant landslides in Valles Marineris. A landslide produces a scarp at the source region and a landslide deposit downhill from the scarp. H₂O and CO₂ as ice or gas can influence mass wasting, for example by sublimating ice that was making particles coherent or sticky, and perhaps by fluidizing the particles so they travel further. Liquid water plays a major role in mass wasting on Earth and has likely done so on Mars as well, for example helping to form the high-latitude gullies.

Major science questions for this theme.

What are the current and past rates of mass wasting for various terrains on Mars?

Do some of the dark slope streaks involve large quantities of water?

What processes trigger large landslides (for example, marsquakes, tectonic oversteepening of slopes, fluvial undercutting of slopes, hydrothermal weakening of the bedrock)?

Can boulder distributions distinguish debris flows from other types of deposits?

Relationship to other science themes. If water is the main focus of the science question, then it would be best to select “fluvial processes” as the main science theme, or perhaps “hydrothermal processes.” Slow viscous relaxation or flow of ice-rich materials is not considered mass wasting because it is too slow—this is best put in the “periglacial” or “glacial” or “polar geology” themes. Mass wasting also occurs in the late stages of forming impact craters, but this should go into the “impact processes” theme. Mass wasting is an important component of landscape evolution, but if a suite of processes affecting landscape morphology is the goal, use the “landscape evolution” theme. Landslide scarps can create excellent exposures of the bedrock, but if that is the main focus then use “sedimentary and layering processes” (if exposing sedimentary rocks) or “geologic contacts/stratigraphy” or “volcanology” (if exposing volcanic rocks) as the main themes. Landslides are often closely associated with tectonic activity, but use “tectonic processes” if that is the main objective. Slope streaks that are monitored to understand seasonal processes can be given the theme “seasonal processes”. Mass wasting would be a good secondary theme in any of the examples given above.

Features of interest potentially visible at HiRISE scale. Boulders! The sizes, shapes, sorting, colors, and distribution of boulders (rocks from ~0.5 m or larger diameter) tell us a great deal about transport processes. For slope streaks or other small mass-wasting features HiRISE might resolve the associated topography or morphologies diagnostic of processes. HiRISE might detect morphologies and colors that help to identify the source region for mass-wasting deposits.