In fluvial geomorphology, an ox bow lake is best described as which of the following types of lakes?

Introduction / Context:
Rivers continually modify their valleys through erosion and deposition. Meandering rivers, in particular, can create distinctive features such as point bars, cut banks, and ox bow lakes. Understanding how ox bow lakes form helps in visualising river dynamics on floodplains. This question asks you to choose the best description of an ox bow lake from several types of lakes created by different geomorphic processes.

Given Data / Assumptions:

• The landform in question is an ox bow lake.
• Options describe lakes formed behind off shore bars, in volcanic craters, from cut off meanders, and in glacial hollows.
• We assume knowledge of how meandering rivers evolve over time.

Concept / Approach:
An ox bow lake forms when a highly curved river meander is abandoned by the main stream. As the river erodes the neck of the meander on the outer banks and deposits on the inner banks, the loop narrows and may eventually be cut through during a flood. The former meander loop is then isolated as a crescent shaped lake, called an ox bow lake because it resembles the curved yoke used on oxen. This process is distinct from lakes formed behind coastal bars, volcanic craters, or glacial erosion.

Step-by-Step Solution:
Step 1: Visualise a meandering river on a flat floodplain, developing large loops over time. Step 2: Erosion occurs on the outer banks of bends, while deposition occurs on inner banks, causing lateral migration of the meander. Step 3: The neck of a meander loop gradually narrows as the river cuts into it from both sides. Step 4: During a flood or high flow event, the river may suddenly break through the narrow neck, creating a new, shorter channel. Step 5: The old loop segment is then cut off from the main channel and becomes a crescent shaped lake, known as an ox bow lake. Step 6: This clearly matches the description of a lake formed due to cut off meander, not a coastal, volcanic, or glacial origin.

Verification / Alternative check:
Standard diagrams in fluvial geomorphology show the evolution from meandering river to cut off loop to ox bow lake and finally to marshy infill. The term ox bow lake is always linked to river meanders and floodplain development. By contrast, lakes behind off shore bars are coastal lagoons, crater lakes form in volcanic depressions, and glacial erosion produces cirques and tarns. The unique curved plan shape of an ox bow lake on a floodplain confirms its origin from a meander cut off.

Why Other Options Are Wrong:

• A lake formed behind an off shore bar: This is a coastal lagoon or bar built lake, not related to river meanders.
• A lake occupying a volcanic crater: This describes a crater lake, formed by volcanic or explosive activity, not fluvial processes.
• A lake occupying a hollow scooped out by a glacier: This refers to glacial lakes such as cirque lakes or rock basin lakes, not ox bow lakes.

Common Pitfalls:
Some students confuse ox bow lakes with glacial lakes because both can appear curved or enclosed on maps. Others may simply not visualise the meander cut off process clearly. To avoid mistakes, remember that ox bow lakes are characteristic of low gradient, meandering rivers on floodplains and are always linked to the abandonment of a former meander loop.

Final Answer:
An ox bow lake is a lake formed when a river meander loop is cut off from the main channel.