PERIGLACIAL LANDFORMS | Paraglacial Geomorphology

Abstract

Paraglacial geomorphology is the study of how nonglacial Earth-surface processes modify glacial landforms, sediments, landsystems, and landscapes following deglaciation. Retreat of glacier ice exposes glacigenic and glacially conditioned sediment sources (rockwalls, drift-mantled slopes, valley-floor glacigenic deposits, and coastal glacigenic deposits) in an unstable or metastable state. Reworking of such sediments may be conceptualized as a sediment cascade, in which source-to-sink transport is interrupted by sediment storage in a range of paraglacial landforms such as talus accumulations, debris cones, alluvial fans, valley fills, deltas, and coastal barrier deposits. Because glacigenic sediment sources are nonrenewable, rates of paraglacial sediment flux can be approximated by an exhaustion model, and paraglacial sediment stores ultimately experience an intrinsic transition from net accumulation to net degradation. Six paraglacial landsystems can be identified, namely those associated with rock-slope adjustment, drift-mantled slopes, glacier forelands, and alluvial, lacustrine, and coastal settings. Paraglacial effects dominate the postglacial geomorphic evolution of most glaciated environments, and paraglacial sediment stores form an abundant source of readily entrainable sediment during periods of glacier expansion. Major Alpine glacial erosional landforms such as cirques, arêtes, and troughs evolve under alternating episodes of glacial and paraglacial landscape modification