How Ice Leaves a Directional Shape
A drumlin is a streamlined hill formed beneath a glacier, often from till—a jumble of clay, sand, gravel, and boulders carried by ice. As a glacier presses against its bed and moves forward, it can deform and reshape this loose sediment into elongated mounds. Some drumlins also contain bedrock or layers of different material, so they are not all built in precisely the same way.
The process is complicated: scientists continue to study how ice, water, and sediment interact to make these forms. But the result is a landscape of hills whose long axes commonly run parallel to the glacier’s movement. Many have a blunter end facing into the former flow and a more tapered end pointing downstream, like a wake left behind a moving object.
Reading a Vanished Glacier’s Path
One hill alone offers limited evidence. A field of drumlins is more revealing: when many neighboring hills share an alignment, that repeated pattern provides a map of ice flow. Researchers compare the hills’ orientation and shape across a region to trace the direction a glacier traveled and how its flow varied across the landscape.
The hills do not record the glacier’s entire history, and local conditions can complicate the pattern. Still, their aligned forms preserve a striking clue long after the ice has melted: a route written into the ground, one hill at a time.
