“…William S. Carlson (1939) measured the flow of some outlet glaciers in the Upernivik region of northeast Greenland in 1931, showing that speed was fastest in the center of the glaciers. His field partner was a young graduate student from the University of Michigan, Max Demorest.…”
Extrusion flow' describes any velocity field where maximum horizontal velocity occurs below the surface. By 1914, viscous flow and basal sliding over rough beds were accepted concepts. Between the world wars, there was little communication between naturalists describing complicated ice sheets, and physicists studying fundamental processes controlling flow. Max Demorest brought concepts from mechanics into glaciology and glacial geology; however, his extrusion flow theory, to explain how ice flowed out of central Greenland, overlooked force imbalance. Rudolf Streiff-Becker found an apparent large imbalance between ice flux discharged through a gate and net accumulation in the upstream catchment at Claridenfirn, Switzerland. Because he underestimated uncertainty in ice depth, he had to propose a strong undercurrent (extrusion flow) to evacuate the excess mass. Reassessment of his assumptions shows that extrusion was actually unnecessary. However, confluence of two lines of evidence for extrusion flow added stature to the concept. In 1952, John Nye showed that free extrusion flow was impossible due to force imbalance. Two forms of extrusion flow survive: capped extrusion flow is possible on local scales where longitudinal stress gradients allow upper ice to move slowly, and rigidbody rotational flow can allow deeper ice to move faster without strain.
DilatationJohann Jakob Scheuchzer, a physicist from Zü rich, proposed the dilatation theory of glacier flow. According to the dilatation theory, meltwater flowed into the interstices and
“…William S. Carlson (1939) measured the flow of some outlet glaciers in the Upernivik region of northeast Greenland in 1931, showing that speed was fastest in the center of the glaciers. His field partner was a young graduate student from the University of Michigan, Max Demorest.…”
Extrusion flow' describes any velocity field where maximum horizontal velocity occurs below the surface. By 1914, viscous flow and basal sliding over rough beds were accepted concepts. Between the world wars, there was little communication between naturalists describing complicated ice sheets, and physicists studying fundamental processes controlling flow. Max Demorest brought concepts from mechanics into glaciology and glacial geology; however, his extrusion flow theory, to explain how ice flowed out of central Greenland, overlooked force imbalance. Rudolf Streiff-Becker found an apparent large imbalance between ice flux discharged through a gate and net accumulation in the upstream catchment at Claridenfirn, Switzerland. Because he underestimated uncertainty in ice depth, he had to propose a strong undercurrent (extrusion flow) to evacuate the excess mass. Reassessment of his assumptions shows that extrusion was actually unnecessary. However, confluence of two lines of evidence for extrusion flow added stature to the concept. In 1952, John Nye showed that free extrusion flow was impossible due to force imbalance. Two forms of extrusion flow survive: capped extrusion flow is possible on local scales where longitudinal stress gradients allow upper ice to move slowly, and rigidbody rotational flow can allow deeper ice to move faster without strain.
DilatationJohann Jakob Scheuchzer, a physicist from Zü rich, proposed the dilatation theory of glacier flow. According to the dilatation theory, meltwater flowed into the interstices and
“…The steady drop in temperature was also noticed in 1948, and it may account for the diminution in glacier speed, if allowance is made for a slight time lag. Forbes, 4 Goldthwait, Finsterwalder and others correlate temperature changes with glacier movement over short periods, although Carlson 5 working in West Greenland, could not find any such relationship. Fig.…”
ABSTRACT. Work on the Froya Gletscher, N.E. Greenland, appears to substantiate the evidence already brought forward for the irregular flow of glaciers over shor t periods. It appears possible to correlate the daily temperature regime with the flow of some "polar glaciers." The distribution of thrust planes seems to have no noticeable effect on the flow. It is suggested that Block-Schollell movement may underlie the jerky motion of some of even the slower moving g laciers. A subglacial stream bed on the Skille Gletscher was explored from the snout for a distance of 500 m. It is estimated that at the farthest point the ice was 76 m. thick. There appears to be good observational eviden ce for de Martonne's theory of medial moraines extending to the bed of the glacier.ZUSAMMENFASSUNG. Arbeiten am Froya Glets cher, Nord Ost Gronland, scheinen den bereits hervorgebrachten Beweis, dass Gletscher in kurzen Zeitraumen unregelmassig fliessen, zu bestatigen. Es scheint moglich zu sein, die tagliche Temperatur-Haushalt mit der Stromung einiger "Polar-Gletscher" in Zusammenhang bringen zu konnen. Die Verteilung von Schubflachen scheint keinen merklichen Einfluss auf die Stromung zu haben. Es wird darauf hingewiesen, dass die Block-Schollen-Bewegung der stossweisen Bewegung einiger, selbst langsam fliessen den G le tscher, zu Grunde liegen mag. Ein subglaziales Strombett am Ski lle Gletscher wurde von der Spitze ausgeh end eine 500 m Strecke weit untersucht. Es wurde geschatzt, dass das E is an der entferntesten Stelle 76 m dick war. Die Martonnesche Theorie, dass mittlere Moranen si ch bis zum Bett des Gletschers erstrecken, sehein t durch Beobachtungen bestatigt zu werden.
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