With reference to Oceanic Deeps or Trenches, consider the following statements: 1. They are the deepest parts of the oceans, located 3-5 km deeper than the surrounding floor. 2. They are tectonically stable regions with no volcanic activity. 3. The Pacific Ocean has the highest number of explored trenches compared to the Atlantic Ocean. Which of the statements given above is/are correct?

The correct option is 1 and 3 only. Explanation Oceanic trenches are long, narrow, and steep-sided depressions found on the ocean floor. They represent the deepest parts of the ocean basins and are typically formed at convergent plate boundaries where dense oceanic lithosphere subducts beneath another plate. Statement-wise Analysis: - Statement 1 is Correct: Trenches are the deepest features of the ocean relief. While the average depth of the ocean floor (abyssal plain) is approximately 3,000 to 6,000 meters, trenches extend significantly deeper, often lying 3 to 5 km below the surrounding floor. For example, the Mariana Trench reaches a depth of nearly 11 km. - Statement 2 is Incorrect: Trenches are not tectonically stable; rather, they are zones of intense tectonic activity. Being located at subduction zones, they are epicenters of strong earthquakes and are closely associated with volcanic activity (forming island arcs or continental volcanic arcs parallel to the trench). - Statement 3 is Correct: The distribution of trenches is uneven across the world's oceans. The Pacific Ocean contains the highest number of trenches (more than 30) due to the "Ring of Fire," a major belt of subduction zones. In contrast, the Atlantic Ocean has far fewer trenches (e.g., Puerto Rico Trench, South Sandwich Trench) because its margins are predominantly passive. Key Takeaway: Oceanic trenches are the deepest parts of the ocean floor, formed at active subduction zones. They are characterized by high tectonic instability, including earthquakes and volcanism, and are most abundant in the Pacific Ocean.

With reference to Oceanic Deeps or Trenches, consi... - NCERT Class 11 Geography MCQ

Solution

The correct option is 1 and 3 only.

Explanation

Oceanic trenches are long, narrow, and steep-sided depressions found on the ocean floor. They represent the deepest parts of the ocean basins and are typically formed at convergent plate boundaries where dense oceanic lithosphere subducts beneath another plate.

Statement-wise Analysis:

Statement 1 is Correct: Trenches are the deepest features of the ocean relief. While the average depth of the ocean floor (abyssal plain) is approximately 3,000 to 6,000 meters, trenches extend significantly deeper, often lying 3 to 5 km below the surrounding floor. For example, the Mariana Trench reaches a depth of nearly 11 km.
Statement 2 is Incorrect: Trenches are not tectonically stable; rather, they are zones of intense tectonic activity. Being located at subduction zones, they are epicenters of strong earthquakes and are closely associated with volcanic activity (forming island arcs or continental volcanic arcs parallel to the trench).
Statement 3 is Correct: The distribution of trenches is uneven across the world's oceans. The Pacific Ocean contains the highest number of trenches (more than 30) due to the "Ring of Fire," a major belt of subduction zones. In contrast, the Atlantic Ocean has far fewer trenches (e.g., Puerto Rico Trench, South Sandwich Trench) because its margins are predominantly passive.

Key Takeaway:
Oceanic trenches are the deepest parts of the ocean floor, formed at active subduction zones. They are characterized by high tectonic instability, including earthquakes and volcanism, and are most abundant in the Pacific Ocean.

NCERT Class 11 Geography — Chapter 1: Water (Oceans)

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