Question

Explain how a glacier can erode the land, and then describe three forms of glacial deposition.

Short answer

Glaciers erode land by plucking and abrasion; they deposit materials forming moraines, drumlins, and eskers.

Step-by-step solution

Understanding Glacial Erosion

A glacier erodes the land primarily through two main processes: plucking and abrasion. Plucking occurs when a glacier freezes onto the rocks beneath it and, as it moves, pulls pieces of rock away with it. This is facilitated by meltwater that seeps into cracks, freezes, and exerts pressure on the surrounding rock. Abrasion happens as the glacier drags the plucked rocks and sediments across the land, scraping and wearing it down much like sandpaper smoothing wood.

Exploring Glacial Deposition

Glacial deposition occurs as the glacier melts, releasing debris it has transported. This consists of materials such as clay, sand, gravel, and boulders. Glacial deposition forms the following three features: 1. **Moraines**: These are accumulations of dirt and rocks that have been pushed along and deposited by a glacier. Moraines form ridges along the edges or snouts of glaciers. 2. **Drumlins**: Streamlined, elongated hill formations formed under glacial ice and composed mostly of glacial till. They indicate the direction of glacier movement. 3. **Eskers**: Long, winding ridges of sand and gravel deposited by meltwater rivers that flowed beneath glaciers. They provide evidence of the paths of subglacial streams.

Key concepts

Plucking

Plucking is a fascinating process by which glaciers erode the land. When a glacier moves, it often attaches itself to the surface of rocks beneath it. The ice acts as a powerful adhesive, freezing around rocks and later pulling them away as the glacier slides forward.
The process begins as meltwater from the glacier seeps into small cracks in the bedrock. This water freezes, expanding and creating pressure against the rock face. Over time, this pressure loosens bits of rock. As the glacier continues its journey, it drags these chunks of rock along, affecting both the landscape below and the glacier's own structure.

Abrasion

Abrasion is akin to nature's version of sanding down surfaces. As the glacier moves, it not only transports loose rocks but also grinds these against the bedrock beneath. Imagine the effect of sandpaper on a plank of wood – this is similar to how abrasion operates.
The rocks and sediments embedded in the glacier's base act as natural tools. They scrape and polish the underlying rock, resulting in a smooth, sometimes grooved landscape. This process can create stunning geological features like striations, which are long, linear scars on rock surfaces, serving as testament to glaciers' abrasive power.

Glacial Deposition

When glaciers melt, they release the debris they carried along their journey. This act of deposition is responsible for unique and varied landforms.
As the glacier loses mass, it deposits various materials like clay, sand, gravel, and enormous boulders. The character of the deposition depends on factors like the glacier's speed, the nature of the materials, and the landscape. Glacial deposition contributes significantly to the reshaping of Earth's surface.

Moraines

Moraines are remarkable features formed by glacial deposition. As glaciers advance and retreat, they accumulate dirt, rocks, and sediment along their paths.
These materials gather in distinct ridges, marking former glacier edges. There are different types: lateral moraines, found along the glacier's sides; terminal moraines, at the glacier's snout; and medial moraines, formed when two glaciers converge. Each moraine type tells a story about the glacier's journey and the sediments' origins.

Drumlins

Drumlins are intriguing landforms made from glacial till, which is unsorted sediments like clay and boulders carved by glaciers. These elongated hills resemble upside-down teaspoons.
Their streamlined shape indicates the direction of ancient glacier movements. The formation process is still debated, but drumlins are essential for interpreting past glacial paths and understanding glacial dynamics. They are often found in groups, forming a landscape known as "drumlin fields."

Eskers

Eskers are remarkable, sinuous ridges reflecting ancient subglacial river paths. During the glacier's life, meltwater rivers form beneath it, carving out tunnels laden with sediment.
As the glacier retreats, these deposits remain as long, winding hills made primarily of sand and gravel. Eskers can stretch for miles and provide valuable insights into glacial hydrology, as well as the direction and flow of the meltwater that shaped them.