A glacier is a river made of ice — except it doesn't flow like water. It creeps. It grinds. It takes a hundred years to move as far as you could walk in an afternoon. How does something so solid manage to flow at all?

It starts with snow. Year after year, snow piles up in a cold mountain valley where summer never gets warm enough to melt it all away. The bottom layers get buried under the weight of all that new snow above. Squeezed and squeezed, the fluffy snow crystals collapse into dense, hard ice.

Once the ice gets thick enough — about as tall as a ten-story building — something strange happens. Ice, which seems perfectly rigid when you hold a cube of it, starts to behave like very, very slow honey. The weight of all that ice above makes the ice below deform and flow.

The ice crystals themselves don't melt. Instead, they slide past each other, grain by grain, rearranging under pressure. It's like a crowd of people in a packed subway car — when the train lurches, everyone shifts a tiny bit, and the whole crowd moves even though each person only budged an inch.

Gravity pulls the glacier downhill. The ice flows fastest in the middle and at the top — sometimes a few feet per day — while the bottom and sides drag against the rock, moving much slower. This difference in speed cracks the surface into deep crevasses, those beautiful, dangerous blue chasms you see in photos.

The bottom of the glacier has a secret weapon: a thin layer of meltwater. The immense pressure down there lowers the melting point of ice, creating a slippery film between the glacier and the bedrock. The glacier skates on its own melt, grinding the rock beneath into fine powder called glacial flour.

As the glacier inches forward, it acts like a giant bulldozer, shoving rocks and soil into piles at its front edge. When the glacier finally melts back — centuries or thousands of years later — it leaves behind these piles, called moraines, as evidence of where it traveled.

So a glacier moves the way ice cream melts off a tilted cone — not by dripping away, but by slowly deforming under its own weight, flowing downhill grain by grain, year by year. The solid river that takes a lifetime to travel a mile.