Glacier surge propagation by thermal evolution at the bed

Bakaninbreen, southern Svalbard, began a prolonged surge during 1985. In 19 86, an internal reflecting horizon on radio echo sounding data was interpre ted to show that the position of the surge front coincided with a transitio n between areas of warm (unfrozen) and cold (frozen) bed. Ground-penetratin g radar lines run in 1996 and 1998 during early quiescence show that the ba sal region of the g-lacier is characterized by a strong reflection, interpr eted as the top of a thick layer of sediment-rich basal ice. Down glacier o f the present surge front, features imaged beneath the basal reflection are interpreted as the bottom of the basal ice layer, the base of a permafrost layer, and local ice lenses. This indicates that this region of the bed is cold. Up glacier of the surge front, a scattering zone above the basal ref lection is interpreted as warm ice. There is no evidence for this warm zone down glacier of the surge front, nor do we see basal permafrost up glacier of it. Thus, as in early surge phase, the location of the surge front is n ow at the transition between warm and cold ice at the glacier bed. We sugge st that the propagation of the front is associated with this basal thermal transition throughout the surge. Because propagation of the front occurs ra pidly and generates only limited heat, basal motion during fast flow must h ave been restricted to a,thin layer at the bed and occurred by sliding or d eformation localized at the ice-bed interface.