Excursus on gravity gliding and gravity spreading

The terms 'gravity gliding' and 'gravity spreading' have long been used to describe deformation driven by gravity alone. However, the traditional defi nitions of these terms cannot be applied unambiguously in many situations. The primary difficulties arise because rocks an not ideally rigid, detachme nt surfaces may not be planar, substrates may be deformable, and rock bodie s do not deform in isolation. The term gravity spreading' is still useful i f it is simply defined as gravity-driven lateral extension and vertical con traction, regardless of basal slope and coherence of the body. I suggest th at the term 'gravity gliding' should be used rarely, and only if the defini ng characteristics are clearly stated and understood. In most cases, more d etailed descriptions should be used instead of, or in addition to, either o f these terms to capture the behavior of rock masses deforming under gravit y. (C) 2001 Elsevier Science Ltd. All rights reserved.