Deglacial meltwater drainage and glaciodynamics: inferences from Laurentide eskers, Canada

This paper evaluates current knowledge of Laurentide eskers in Canada in th e light of developments in glacier hydrology and glacial sedimentology. Que stions regarding the morpho-sedimentary relations of eskers, the synchronei ty and operation of R-channel systems, the role of supraglacial meltwater i nput and proglacial water bodies, the controls on esker pattern, and the gl aciodynamic condition of the ice sheet at the time of esker formation are d iscussed. A morphologic classification of eskers is proposed. Five types of eskers are identified and investigated. Type I eskers Likely formed in ext ensive, synchronous, dendritic R-channel networks under regionally stagnant ice that terminated in standing water. Type II eskers likely formed in sho rt, subaqueously terminating R-channels or reentrants close to an ice front or grounding line that may have actively retreated during esker sedimentat ion. Type III askers plausibly formed in short R-channels that drained eith er to interior lakes in, or tunnel channels under, regionally stagnant ice. Type IV eskers may have formed as time-transgressive segments in short, su baerially terminating R-channels (or reentrants) that developed close to th e ice margin as the ice front underwent stagnation-zone retreat or downwast ed and backwasted regionally (stagnant ice); however, formation in synchron ous R-channels cannot be discounted on the basis of reported observations. Type IV eskers may have formed in H-channels that terminated subaerially. T he spatial distribution of these esker types is discussed. The factors that determined Laurentide R-channel pattern and operation were likely a comple x combination of (i) supraglacial meltwater discharge, (ii) the number and location of sink holes, (iii) the ice surface slope, thickness and velocity , and (iv) the permeability, topography and rigidity of the bed. These fact ors cause and respond to changes in ice dynamics and thermal regime over th e glacial cycle. (C) 2000 Elsevier Science B.V. All rights reserved.