A long, winding ridge of stratified sand and gravel is known as:
esker
Understanding Glacial Landforms: The Esker Explained
The question asks to identify a specific geological feature: a long, winding ridge composed of stratified sand and gravel. This type of landform is a direct result of glacial activity and deposition.
Analyzing the Options
Let's look at the provided options and see which one matches the description of a long, winding ridge of stratified sand and gravel:
- whorl: A whorl typically refers to a circular or spiral arrangement, not a geological ridge.
- esker: An esker is specifically defined as a long, winding ridge composed of stratified sand and gravel, deposited by meltwater streams flowing within or beneath a melting glacier. This perfectly matches the description.
- lop: 'Lop' is not a standard geological term for a landform or ridge.
- arch: An arch is a curved structure, often found in rock formations, but it is not described as a long, winding ridge of stratified sand and gravel formed by glacial processes.
Based on the definitions, the term that accurately describes a long, winding ridge of stratified sand and gravel is an esker.
Formation of Eskers
Eskers are formed by streams that flow within ice tunnels, beneath, or on top of a glacier. As the glacier melts, these streams carry sediment (sand and gravel). When the velocity of the meltwater stream decreases or when the glacier retreats, the sediment is deposited within the ice tunnel or channel. After the surrounding ice melts completely, the deposited sediment forms a raised, sinuous ridge on the landscape. The sorting and layering (stratification) of the sediment occur because it was deposited by flowing water, which separates particles based on size and density.
| Term | Description | Matches Question? |
|---|---|---|
| Whorl | A spiral or circular pattern. | No |
| Esker | A long, winding ridge of stratified sand and gravel deposited by glacial meltwater. | Yes |
| Lop | Not a geological landform term. | No |
| Arch | A curved structure, often erosional. | No |
Revision Table: Glacial Depositional Landforms
| Landform | Description | Composition | Formation Process |
|---|---|---|---|
| Esker | Long, winding ridge | Stratified sand and gravel | Deposited by meltwater streams within or beneath ice |
| Kame | Irregularly shaped hill or mound | Stratified sand and gravel | Deposited by meltwater in contact with ice (e.g., in crevasses, ice-walled lakes) |
| Drumlin | Elongated, streamlined hill (blunt end faces direction of ice flow) | Till (unsorted mixture of sediment) | Shaped by ice flowing over existing sediment |
| Moraine | Ridge or mound of till | Till (unsorted) | Deposited directly by ice (e.g., terminal, lateral, medial moraines) |
Additional Information on Eskers and Glacial Geology
Eskers are prominent features in areas previously covered by glaciers, particularly continental ice sheets. They can range in length from a few meters to hundreds of kilometers and can be tens of meters high. Their sinuous path often reflects the course of the meltwater stream that formed them, which was controlled by the pressure and flow within the ice. Eskers are valuable resources for sand and gravel because their sediment is often well-sorted. Studying eskers helps geologists understand the dynamics of ancient ice sheets and the path of meltwater flow.
Compared to other glacial features:
- Unlike drumlins or moraines, which are typically composed of unsorted till (sediment deposited directly by ice), eskers are made of stratified sand and gravel because they are deposited by flowing water, which sorts sediment.
- Kames are also made of stratified sand and gravel but are typically more irregular mounds or hills, formed in different depositional environments related to melting ice.
Therefore, the unique combination of being a long, winding ridge and being composed of stratified sand and gravel distinctly identifies this landform as an esker.
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