Bear Glacier, Alaska

This image taken in 2005 of Bear Glacier highlights the beautiful color of many glacial lakes.

The hue is caused by the silt that is finely ground away from the valley walls by the glacier and deposited in the lake. The particles in this “glacial flour” can be very reflective, turning the water into a distinctive greenish blue. The lake, eight miles up from the terminus of the glacier, was held in place by the glacier, but in 2008 it broke through and drained into Resurrection Bay in Kenai Fjords National Park.
The grey stripe down the middle of the glacier is called a medial moraine. It is formed when two glaciers flow into each other and join on their way downhill. When glaciers come together, their lateral moraines, long ridges formed along their edges as the freeze-thaw cycle of the glacier breaks off chunks of rock from the surrounding walls, meet to form a rocky ridge along the center of the joined glaciers.

Image: GeoEye/NASA, 2005.