Viewing Earth’s surface as a soft-matter landscape

Abstract

Earth’s surface is composed of a staggering diversity of particulate–fluid mixtures: dry to wet, dilute to dense, colloidal to granular and attractive to repulsive particles. This material variety is matched by the range of relevant stresses and strain rates, from laminar to turbulent flows and steady to intermittent forcing, leading to anything from rapid and catastrophic landslides to the slow relaxation of soil and rocks over geologic timescales. From a physics point of view, virtually all Earth and planetary landscapes are composed of soft matter, in the sense that they are both deformable and sensitive to collective effects. Geophysical materials, however, often involve compositions and flow geometries that have not yet been examined in physics. In this Review, we explore how a soft-matter physics perspective has helped to illuminate, and even predict, the rich dynamics of earth materials and their associated landscapes. We also highlight phenomena of geophysical flows that challenge, and will hopefully inspire, work on more fundamental aspects of soft matter.