How do drumlins record former ice flow?
A drumlin is a streamlined hill shaped beneath a glacier and elongated along ice flow. Drumlins commonly occur in similarly aligned groups, helping reconstruct former ice movement.
Shaping beneath the ice
Drumlins often consist of glacial sediment, although some contain bedrock cores or varied internal layers. Deformation, erosion and deposition beneath ice can act together. A single simple formation model does not explain every drumlin. One end is commonly blunter and the other more elongated, but shapes vary and do not always match textbook profiles.
Checking the directional evidence
Long axes can indicate the general alignment of former flow. To determine its actual direction, investigators combine end shapes with rock scratches and neighbouring glacial features. Later advances may have reshaped older forms. Identifying an elongated hill as a drumlin therefore requires its internal material and surrounding context, not its outline alone. Such evidence is particularly useful on broad plains where former ice sheets have disappeared.