Evolution of subglacial water pressure along a glacier’s length

• Published in: Annals of Glaciology
• Main Authors: Harper, Joel T., Humphrey, Neil, Pfeffer, W. Tad, Fudge, T. J., O'Neel, Shad
• Format: Text
• Language: unknown
• Published: ScholarWorks at University of Montana 2005
• Subjects: glaciology; Bench Glacier; subglacial water-pressure; Earth Sciences; Long Glacier; glacier; Alaska
• Online Access: https://scholarworks.umt.edu/geosci_pubs/29; https://doi.org/10.3189/172756405781813573; https://scholarworks.umt.edu/context/geosci_pubs/article/1029/viewcontent/Evolution_of_subglacial_water_pressure_along_a_glacier_s_length.pdf

Observations from along the length of Bench Glacier, Alaska, USA, show that the subglacial water-pressure field undergoes a multiphase transition from a winter mode to a summer mode. Data were collected at the glacier surface, the outlet stream, and in a network of 47 boreholes spanning the length of the 7 km long glacier. The winter pressure field was near overburden, with low-magnitude (centimeter to meter scale) and long-period (days to weeks) variations. During a spring speed-up event, boreholes showed synchronous variations and a slight pressure drop from prior winter values. Diurnal pressure variations followed the speed-up, with their onset associated with a glacier-wide pressure drop and flood at the terminus stream. Diurnal variations with swings of up to 80% of overburden pressure were typical of mid-summer. Several characteristics of our observations contradict common conceptions about the seasonal development of the subglacial drainage system and the linkages between subglacial hydrology and basal sliding: (1) increased water pressure did not accompany high sliding rates; (2) the drainage system showed activity characteristic of the spring season long before abundant water was available on the glacier surface; (3) the onset of both spring activity and diurnal variations of the drainage system did not show a spatial progression along the length of the glacier.