For more than half a century, scientists and polar explorers have puzzled over the origin of serrated zipper-like patterns that sometimes form when floating ice sheets collide.
When two ice sheets driven by wind and ocean currents collide, one will often ride up over the other. But occasionally the edges of the sheets mesh together in an arrangement of interlacing, roughly rectangular protrusions a meter or so wide.
If the colliding sheets are equally thick, their ripples have the same wavelength, according to the new theory. They also have opposite phase--where one sheet rises up, the other sags down--because the sheets bent in opposite directions at the point of contact. As the corrugated sheets press together, fractures running roughly perpendicular to the edge set in at the points of direct contact. The "fingers" of material between the fractures then push over and under each other and create the zipper-like pattern.
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