SEDIMENTARY PROCESSES/Catastrophic Floods 631 Figure Ice dammed lake storage locations Letters A I represent different meltwater storage locations, each associated with characteristic lake drainage triggers and jokulhlaup routing characterics ‘A’ represents a tributary glacier which dams a trunk valley and which is subject to subaerial breach widenin ‘B’ ‘D’ ‘E’ ‘F’ and ‘G’ represent proglacial and ice marginal ice dammed lakes in a variety of settings where drainage is triggered by mechanisms such as lake overspill, ice dam flotation, syphoning and subglacial cavity formation ‘C’ represents a supraglacial lake which taps through the entire thickness of the glacier ‘H’ is a subglacial lake within either a suitable storage location such as a volcanic caldera, or as an up turned bowl shaped lake often associated with locations with high geothermal acitivity Drainage triggers postulated for subglacial lakes include ice dam flotation as well as Darcian flow through the glacier substrate ‘I’ represents a subglacial eruption site, which may result in little or short lived meltwater storage during the course of an eruption High meltwater temperatures associated with the drainage of geothermal and volcanic events characteristically result in jokulhlaups with rapid rising stages Jokulhlaup hydrographs have a longer rising stage and lower peak discharge the further the ice dammed lake is from the glacier snout After Tweed and Russell (1999) Controls on the formation and sudden drainage of glacier impounded lakes: implications for jokulhlaup characteristics Progress in Physical Geography 23: 79 110 Figure Relationships between lake volume and peak discharge for the failure of different dam types After Costa (1988) Rheologic, geomorphic and sedimentological differentiation of water floods, hyperconcentrated flows, and debris flows In: Baker VR, Kochel RC, and Patton PC (eds.) Flood Geomorphology, pp 113 122 London: Wiley