Question

The rise and fall of the general sea level due to melting or forming of the glaciers is known as ___________ movement.
 

• A. Iso-static
• B. Eustatic
• C. Ice
• D. Glacier

Hint:

To remember the difference, think: {E}ustatic = {E}verywhere (global sea level). {I}sostatic = {I}solated (local land level).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The question asks for the geological term that describes global changes in sea level. There are two main types of sea-level change.
Step 2: Detailed Explanation:
- Eustatic change: This refers to a global change in the amount of water in the oceans or a change in the shape of the ocean basins. The melting of glaciers and ice sheets during warmer periods (interglacials) releases vast amounts of water into the oceans, causing a global sea-level rise. Conversely, the formation of glaciers during ice ages locks up water, causing a global sea-level fall. This is a eustatic movement.
- Isostatic change: This refers to a local change in land level relative to the sea. For example, the immense weight of an ice sheet can depress the landmass beneath it. When the ice melts, the land slowly rebounds upwards over thousands of years. This is a local phenomenon and is called isostatic rebound or glacio-isostasy.
- The question describes a change in the "general sea level," which implies a global effect, correctly identified as eustatic.
Step 3: Final Answer:
The global rise and fall of sea level caused by the melting and forming of glaciers is known as eustatic change.