Glaciers have a garbage problem. Bits of rock, ranging in size from powdery glacier flour to large boulders, are carved from the valley floor and walls by the flowing ice and deposited as moraines along the edges and on top of the glacier. Glacial till is the name for this unsorted mix of clay, silt, sand, gravel, and boulders.

Moraines are named after their location; a collection of debris at the snout of a glacier is called a terminal moraine. Blue Glacier has deposited most of the debris collected up glacier in a 50-meter high lateral moraine that follows nearly 900 meters of the right flank. This monstrosity was likely deposited over a number of separate glacial advances when the thickness of the ice was much greater.

A second type of moraine found on the Blue is a medial moraine. Here, debris is deposited on top of the glacier’s surface. Medial moraines originate when an ice stream picks up rock from an outcrop and carries it into the body of the glacier. Some years a medial moraine marks the longitudinal septum. Two medial moraine ribbons run parallel to the glacier’s right margin.



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Benjamin Drummond 2002