Question

What does a valley glacier create at the point where it starts? A) esker C) till B) moraine D) cirque

Short answer

D) Cirque is created at the starting point of a valley glacier.

Step-by-step solution

Understand the Options

Read the question carefully and note the options available: A) esker, B) moraine, C) till, D) cirque. Each term is a geomorphological feature related to glaciers. We need to identify which one is created at the starting point of a valley glacier.

Define a Valley Glacier

A valley glacier is a stream of flowing ice confined within a valley. It typically forms in mountainous regions where sufficient snowfall accumulates over time, compacting into ice.

Recognizing Cirque Formation

A cirque is a bowl-shaped depression on a mountain where a valley glacier begins to form. It is created by the erosion and weathering action of the glacier at its head, making it the starting feature of many valley glaciers.

Verify Other Options

To ensure accuracy, verify other options: - An esker is a long ridge of sediment deposited by meltwater streams under glaciers. - Till is unsorted glacial debris deposited directly by melting glaciers. - A moraine is an accumulation of dirt and rocks that have fallen onto the glacier surface or been pushed along by the glacier. None of these are formed specifically at the starting point of a valley glacier.

Conclude

Based on the definitions and characteristics, the correct answer is D) cirque. Valley glaciers originate at cirques, which are eroded by the glacier's initial activity.

Key concepts

Cirque

A cirque, pronounced like "serk," is a natural amphitheater found in mountainous regions where valley glaciers originate. Imagine a shallow, yet colossal bowl carved out of a mountain. This bowl-like hollow is a cirque, and it's where the magic of glacier formation begins.
When snow accumulates in these high-altitude basins, it eventually compresses into ice, forming a glacier. Over time, this accumulated ice begins to move and erode the basin further, deepening and enlarging the cirque.

• Cirques are characterized by their steep headwalls and their semi-circular or concave shape.
• They often have a tarn, which is a small lake formed by melting glacier ice, at their base.
• Cirques are sometimes called "corries" or "cwms," especially in British and Scottish contexts.

By understanding cirques, you can appreciate the early stages of glacial development, highlighting the immense force glaciers exert on their surroundings.

Glacial Landforms

Glacial landforms are the sculpted results of glacial activity on land. These features tell the story of past glacial movements and the powerful forces that shaped them.
Each landform occurs in different stages and parts of a glacier's life cycle, from its creation in a cirque to its advance or retreat across a landscape.
Let's delve into some key glacial landforms:

• Moraines - These are accumulations of rock and soil debris deposited by a glacier. Moraines can be found along the sides and terminal ends of a glacier.
• Eskers - Formed by meltwater streams beneath glaciers, eskers are snaking ridges of sand and gravel.
• Drumlins – Smooth, elongated hills composed of glacial till, indicating glacier movement direction.
• Kettles - Depressions left after large ice chunks melt, often forming ponds or small lakes.

Understanding these landforms helps geologists reconstruct past glacial periods and landscape transformations.

Glacial Erosion

Glacial erosion is the process responsible for shaping much of the Earth's spectacular mountainous regions. It occurs when a glacier moves over bedrock, eroding the landscape through sheer force. There are three primary erosion processes involved: plucking, abrasion, and freeze-thaw.

• Plucking - This is when a glacier lifts chunks of rock from the ground as it flows, a process intensified by freezing and thawing cycles.
• Abrasion - As a glacier drags its sediment and debris across the land, it acts like a sandpaper, smoothing the rock surface beneath.
• Freeze-Thaw - Water seeps into cracks, freezes, and expands, eventually breaking chunks of rock, which the glacier then erodes away.

These erosion techniques create remarkable features including cirques, as well as U-shaped valleys and striations. These physical transformations are evidence of the tremendous power glaciers wield as agents of erosion.