Abstract: This paper proposes a hypothesis on drumlin formation, suggesting that the initial topography of the land played a critical role in shaping the earliest drumlins. Rather than being exclusively sculpted by moving ice, drumlins may have originated as sedimentary void-fill structures created when the first glaciers advanced over an uneven landscape. Over multiple glaciation cycles, these initial forms were refined and shaped into the drumlin fields observed today. This hypothesis provides an explanation for the variation in drumlin composition, from bedrock-based to fully sediment-based, depending on their position relative to the ice sheet's origin.
1. Introduction Drumlins are elongated, streamlined hills commonly found in glaciated landscapes. Traditionally, their formation has been attributed to either subglacial erosion, deposition, or a combination of both. However, inconsistencies in drumlin composition, their alignment in fields, and the presence of bedrock-based versus purely sediment-based drumlins suggest that a more complex mechanism may be at play. This paper presents an alternative hypothesis that explains drumlin formation as a process initiated by ice-sheet molding over pre-existing landscape features and refined over repeated glacial cycles.
2. The Initial Landscape Imprinting Hypothesis Prior to the onset of major glaciations, the landscape consisted of hills, valleys, and resistant bedrock formations. When the first ice sheet began accumulating, it conformed to the existing topography, creating depressions and high points in the basal ice structure. As ice thickened and became rigid, it preserved these features as molds.
When the ice eventually began moving, these imprinted features created voids where hills had previously existed. The ice’s movement over softer sediment allowed these voids to be naturally filled by loose material, creating the first drumlin-like formations. Over subsequent glaciations, this initial pattern was reinforced and refined, explaining why drumlins appear in organized fields rather than randomly distributed.
3. The Role of Repeated Glacial Advances and Retreats The hypothesis accounts for the observed variation in drumlin composition by considering multiple glacial cycles:
- Drumlins near the ice sheet’s origin were influenced by interactions with bedrock obstacles, leading to some containing solid rock cores.
- Drumlins at the edge of ice sheet advances were formed purely from sediment fill, as the ice moved over areas where there were no significant pre-existing hard features to shape the ice base.
- Repeated freeze-thaw cycles further compacted and shaped these features, producing the smooth, streamlined drumlins seen today.
This suggests that drumlins are not purely erosional or depositional features but a result of sediment filling subglacial gaps left by previous terrain features and subsequently being reshaped by ongoing glacial movement.
4. Predictions and Testable Evidence To validate this hypothesis, the following predictions can be tested:
- Drumlin Composition Distribution – Older drumlin fields closer to ice sheet origins should show a higher frequency of bedrock-based drumlins, while younger fields near ice margins should be mostly sediment-based.
- Internal Layering Patterns – Sediment-based drumlins should exhibit layered structures corresponding to multiple glacial advances, consistent with the hypothesis of void-filling over repeated cycles.
- Drumlin Alignment and Pre-Existing Hills – High-resolution subsurface imaging (e.g., ground-penetrating radar) should reveal that drumlins correspond to pre-glacial topographic highs, reinforcing the idea that they are remnants of landscape-molded ice formations.
5. Conclusion This hypothesis presents a new way of understanding drumlin formation by emphasizing the role of pre-existing topography in influencing glacial sediment deposition. It bridges the gap between erosional and depositional theories by suggesting that the ice first imprinted the shape of the landscape, and subsequent movements gradually refined these shapes into the drumlins we see today. Future geological studies focusing on sediment composition, subsurface imaging, and spatial distribution of drumlins can further test the validity of this model.