Environment 360: Melting and refreezing at the base of the Greenland ice sheet has created massive, complex structures the height of skyscrapers and the width of Manhattan, according to research published in Nature Geoscience. The hidden formations more than a mile below the surface stand in stark contrast to the nearly flat, smooth exterior of the ice sheet and may accelerate its flow toward the sea, researchers say. Scientists had previously interpreted the irregular topography at the base of the ice as hills or...