Question

In a gravity survey that is being carried out in the vicinity of a large mountain, it was observed that the deflection of the plumb line from the vertical is less than what is calculated using the visible mountain mass. Which one of the inferences about the mountain is correct?

• A. It has a high-density root
• B. It has no root
• C. It has a low-density root
• D. It has a high-density anti-root

Hint:

In gravity surveys, a mountain with a low-density root results in less gravitational pull than expected, due to isostatic compensation.

Answer 1

The Correct Option is C

Step 1: Concept of isostasy and gravity anomalies. 
Large mountains are typically compensated by a less dense root extending into the mantle — like an iceberg floating in water. 
Step 2: Explaining the smaller-than-expected gravitational effect. 
If the observed gravitational deflection is less than what’s expected from the visible mass, it implies a mass deficiency beneath — i.e., a low-density root is counteracting the mountain’s gravitational pull.