Landslides in the Solar System

Abstract

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article. Landslides are gravity-driven mass movements of rock, earth, or debris. All of these surface processes occur under the influence of gravity, meaning that they globally move material from higher to lower places. Outside Earth, these structures were first observed in a lunar crater during the Apollo program, but mass movements have been spotted on several rocky worlds (solid bodies) in the solar system, including icy satellites, asteroids, and comets. On Earth, landslides have the effect of shaping the landscape more or less rapidly, leaving a signature that is recognised through field surveys and visual analysis, or automatic identification, on aerial photographs or satellite images. Landslides observed on Earth and in solid bodies of the solar system are of different types on the basis of their movement and the material involved in the failure. Material is either rock or soil (or both) with a variable fraction of water or ice; a soil mainly composed of sand-sized or finer particles is referred to as earth, while it is called debris if composed of coarse fragments. The landslide mass may be displaced in several types of movement, classified generically as falling, toppling, sliding, spreading, or flowing. Such diverse characteristics mean that the size of a landslide (e.g., area, volume, fall height, length) can vary widely. For example, on Earth, their areas range up to eleven orders of magnitude, while their volumes vary by eighteen orders, from small rock fragments to huge submarine landslides. The classification of extraterrestrial landslides is based on terrestrial analogs, which have similarities and characteristics that resemble those found on the planetary body. This morphological classification is made regardless of the geomorphological environment or processes that may have triggered the slope failure. Comparing landslide characteristics on various planetary bodies helps to understand the effect of surface gravity on landslide initiation and propagation, which can be of tremendous importance when designing manned and unmanned missions with landings on extraterrestrial bodies. Regardless of the practical applications of such study, knowing the morphology and surface dynamics that shape solid bodies in the space surrounding the Earth is something that has fascinated the human imagination since the time of Galileo.