Abstract An important paradigm in geomorphology is paraglacial sedimentation , a phrase first used almost 40 years ago to describe reworking of glacial sediment by mass wasting and streams during and after continental-scale deglaciation. The concept has been extended to include non-glacial landforms and landscapes conditioned by glaciation. In this paper we apply the paraglacial concept to volcanoes in southern British Columbia, Canada, that formed, in part, in contact with glacier ice. The Cheekye River basin, a small watershed on the flank of a volcano that erupted against the decaying Cordilleran ice sheet, has a Holocene history marked by an exponential decay in debris-flow activity and sediment yield. Its history is consistent with the primary exhaustion model of the paraglacial cycle. At larger spatial scales, this primary sediment is reworked by rivers and transported downstream and augmented by stochastic geomorphic events. Repeated large landslides from Mount Meager volcano in southern British Columbia have delivered a disproportionate volume of sediment to the fluvial system: although occupying only 2% of the watershed area, 25–75% of the 10 km 3 of sediment deposited in Lillooet River valley during the Holocene originated from the volcano. In these cases a significant overall reduction in sediment yield must await the removal, by erosion, of volcanic edifices, a process that could take up to millions of years. These examples of paraglacial activity on Quaternary volcanoes are end members in the spectrum of landscape response to Pleistocene deglaciation.

Abstract The purpose of this paper is to examine the internal architecture and post-glacial evolution of Cheekye fan, British Columbia, Canada. Analysis of a large database of ground penetrating radar (GPR) profiles has allowed the identification of ten reflection configurations that characterize this high-energy environment. GPR profiles augmented with test-pit, well-log and radiocarbon data provided detailed subsurface information and revealed the large-scale internal architecture and Holocene sedimentation history of Cheekye fan. Based on a shift in reflection configuration with depth, GPR data appears to record a change in the mode of deposition through time. This data suggests that Cheekye fan is a paraglacial fan, largely a product of the geological past. This fact should be taken into consideration when making future hazard estimates.

Abstract A cluster of exceptionally large sediment fans occurs in Val Venosta, a glacial trough in the east-central Alps, Italy. Its 59 tributary valleys generate 49 fans with volume:catchment area ratios varying across four orders of magnitude. Geomorphological and statistical analysis distinguish ‘allometric’ and ‘anomalous’ fans. Catastrophic massive slope failure origins are suggested for the anomalous cases. They comprise ‘outsize fans’ and ‘megafans’, the latter attaining 400 m cone height and 2700 m radius, and dominating the trough. Above most fans, evidence is found for source cavities of comparable volume. Reconstruction of the missing sides and heads of two tributary valleys reveals lost mountains 700 m deep. They are credible sources for the Malser Haide, a globally significant 11 km-long megafan with an estimated volume of 1650 Mm 3 , and the St Valentin outsize fans. Generally, anomalous fans occur where landslides are funnelled, comminuted and controlled through ‘debouchures’ high enough above the trough floor for conoidal deposition. Although sedimentological data are sparse, these fans may represent a new category of catastrophic slope failure outcome, mimicking conventional sediment fans of incremental origin. The Val Venosta cluster is the largest in the Alps, with concentrated glacial erosion in conducive geology among the possible factors explaining anomalous fan incidence.