Though it is all composed of frozen water, ice is not uniform. On 7 October this image was taken of a variety of ice types off the coast of East Antarctica. Brilliant white ice fills the right half of this image. It is fast ice, and derives its name from the fact that it holds fast to the shore. This ice is thick enough to completely hiden the underlying seawater, hence its brilliant white colour. Trapped within the fast ice, and stuck along the edge of it, are icebergs. Ice shelves can range in thickness from tens to hundreds of meters, and the icebergs that calve off of them can tower over nearby sea ice. The water-saturated ice leaves a blue tinge. The icebergs along the edge of the fast ice are likely grounded on the shallow sea floor, and their presence may help hold the fast ice in place. Farther out to sea is pack ice that drifts with winds and currents. Much thinner than the fast ice, the translucent pack ice appears in shades of blue-grey

Photograph: ALI/E-O1/NASA