Ogives of the East Twin Glacier, Alaska Their Nature and Origin

The perfection, fine exposure, and unusual accessibility of ogives on East Twin Glacier, Alaska, make this an exceptional place in which to study the nature and origin of this phenomenon. The origin of ogives is discussed, and previous hypotheses are critically analyzed. With the exception of a hypothesis first suggested by R. T. Chamberlin, that ogives are the surficial expressions of shearing planes, no other hypothesis satisfactorily accounts for the fact that these ogives are exposed edges of layers of denser and dirtier ice than the intervening layers. Concepts of glacier flow evolved by Demorest provide a reasonable mechanism for understanding their formation, namely, periodic obstructed extrusion flow down-glacier from an icefall. Debris which was originally basal is believed to become, by upthrusting and ablation, the surface manifestation of an ogive.