Depositional Landforms of Glaciers

Imagine you are in a vast, icy landscape where a glacier is retreating after centuries of slow movement. As it melts, it leaves behind a chaotic mix of rocks, sand, and silt—like a construction site abandoned by nature. This is glacial deposition, a process where glaciers, after eroding landscapes, act as transporters and depositors of sediment, shaping landforms that last for thousands of years.

Let’s explore the fascinating world of depositional landforms, understanding how glaciers don’t just carve landscapes but also build them.

Moraines

Think of a glacier as a giant bulldozer pushing rocks, gravel, and sand along its path. When the glacier melts or retreats, it drops these materials in different patterns, creating moraines. Moraines are the most common glacial depositional features, forming ridges or mounds of glacial debris.

Types of Moraines:

• Terminal Moraine: Imagine a glacier acting like a conveyor belt, carrying debris forward. When it reaches its maximum extent and starts melting, the debris piles up at the glacier’s end, forming a ridge-like structure. This is a terminal moraine—a clear marker of where the glacier once stood.
  • Example: The Long Island terminal moraines in New York, USA.
• Lateral Moraine: As glaciers move, they scrape and collect debris from the valley walls. This debris accumulates along the sides of the glacier, forming lateral moraines—long ridges running parallel to the glacier’s path.
  • Example: Lateral moraines are commonly seen in the Alps and the Himalayas.
• Medial Moraine: When two glaciers merge, their lateral moraines combine in the middle, forming a dark ridge of debris along the glacier’s center. This is a medial moraine, marking the confluence of two glaciers.
  • Example: The Baltoro Glacier in the Karakoram Range, Pakistan.

After the glacier melts, these moraines remain as evidence of the glacier’s past journey, shaping the valleys we see today.

Drumlins

Now, let’s move to an area where the ground is covered with smooth, rounded hills that look like upside-down boats or spoons. These are drumlins, unique landforms created by glacial deposition.

How Are Drumlins Formed?

The exact formation of drumlins is still debated, but a common explanation is:

• As glaciers advance, they reshape older deposits of glacial till (unsorted sediment left by ice).
• The advancing glacier erodes the steeper (up-glacial) side and deposits material on the gentler (down-glacial) side, giving drumlins their characteristic asymmetrical shape.
• Over time, multiple drumlins form in clusters, creating what is called “Basket of Eggs” topography—a landscape covered with these rounded hills, resembling a basket filled with eggs.

Where Are Drumlins Found?

• Finland, Northern Ireland, and Wisconsin (USA) are famous for their drumlin fields.
• The Elgin and Drumlin Belt in Scotland is another well-known example.

Impact on Drainage

Drumlin fields disrupt river flow, making drainage patterns irregular. Rivers and streams often struggle to find a defined path, creating swamps, marshes, and lakes between drumlins.

Conclusion

Depositional landforms like moraines and drumlins are evidence of the glacier’s immense power—not just in eroding landscapes but also in shaping new ones.