In this film slide, Alaska’s Smith Glacier looms cold and blue in its blanket of mist and fog. As our vessel drifted quietly across the water through the still, damp air, every groan, creak and crackle of the ice could be heard. Water flows downhill even in solid form, because under enough pressure, ice behaves like a very slow-moving fluid. Powerful erosion agents, glaciers snag rocks and boulders, then grind them against each other or the ground until all the resulting material is dropped, either by melting or breakage (calving) of the ice. The dark streak in the middle is a medial moraine, made of a mix of ice and dark rock debris that had been carried along the inside edges of two smaller glaciers, before they merged to form this one.