Unit 3 - Essays - Plate Tectonics UPDATED

Question 1

“With the aid of examples, assess the extent to which subduction is involved in the formation of tectonic landforms.”

Answer 1

Main Body Paragraph 1: The Role of Subduction in Forming Volcanic Landforms
Key Point: Subduction is a major cause of volcanic activity at destructive plate boundaries.
Explanation:
At destructive boundaries, denser oceanic plates subduct beneath lighter continental or oceanic plates.
The descending plate melts due to friction and mantle heat, creating magma that rises to form volcanoes.

Examples & Evidence:
The Andes Mountains (South America):
Formed by the subduction of the Nazca Plate beneath the South American Plate at a rate of 7–9 cm per year.
Includes active volcanoes like Cotopaxi and Ojos del Salado.
The Pacific “Ring of Fire”:
Hosts 75% of Earth’s volcanoes due to extensive subduction zones.
Mount St. Helens (USA) and Mount Fuji (Japan) as key examples.
Scale and Temporal Variation:
Volcanic arcs span thousands of kilometers and develop over millions of years.
Continuous subduction leads to prolonged volcanic activity and large-scale volcanic arcs.
Link to the Question:
Demonstrates how subduction is crucial for volcanic landforms, highlighting its significant impact.

Main Body Paragraph 2: Subduction and the Formation of Ocean Trenches
Key Point: Subduction directly forms deep oceanic trenches at convergent plate boundaries.
Explanation:
When an oceanic plate subducts beneath another plate, it pulls the seafloor down, forming deep trenches.
The angle and speed of subduction influence trench depth and shape.

Examples & Evidence:
Mariana Trench (Pacific Ocean):
Deepest trench at 10,994 meters (Challenger Deep).
Formed by the Pacific Plate subducting beneath the Mariana Plate.
Peru-Chile Trench:
Extends for 5,900 kilometers off the western coast of South America.
Formed by the subduction of the Nazca Plate beneath the South American Plate.
Scale and Temporal Variation:
Trenches form over millions of years, deepening progressively as subduction continues.
The depth can exceed 11 kilometers, demonstrating the large-scale impact of subduction.
Link to the Question:
Highlights subduction’s critical role in trench formation, showing its impact on oceanic landscapes.

Main Body Paragraph 3: Limited Role of Subduction in Mid-Ocean Ridge Formation
Key Point: Mid-ocean ridges are formed by divergent plate boundaries, not subduction.
Explanation:
Mid-ocean ridges occur where plates move apart, allowing magma to rise and solidify, forming new oceanic crust.
No subduction is involved as plates are spreading rather than converging.

Examples & Evidence:
Mid-Atlantic Ridge:
Extends over 16,000 kilometers, separating the Eurasian and North American plates at 2 cm per year.
Key locations: Iceland, where the ridge is exposed above sea level.
East Pacific Rise:
Fast-spreading ridge with rates of 6–16 cm per year, showing the scale and speed of non-subductive processes.
Scale and Temporal Variation:
Spreads over thousands of kilometers and evolves continuously as plates diverge.
Represents one of the largest geological features on Earth.
Link to the Question:
Demonstrates that subduction is not involved in all tectonic landforms, highlighting limitations in its influence.

Main Body Paragraph 4: Rift Valleys and the Absence of Subduction
Key Point: Rift valleys are formed by divergent forces on land, not subduction.
Explanation:
Rift valleys occur when continental plates stretch and thin, causing the crust to fracture and sink.
No downward movement of one plate beneath another is involved.

Examples & Evidence:
East African Rift Valley:
Extends about 6,400 kilometers from Syria to Mozambique.
Formed by the African Plate splitting into the Nubian and Somali subplates at 0.5 cm per year.
Features volcanoes like Mount Kilimanjaro due to upwelling magma, not subduction.
Baikal Rift Valley (Russia):
Deepest continental rift at 1,642 meters, formed by extensional tectonics without subduction.
Scale and Temporal Variation:
Develops over millions of years with large-scale faults and deep valleys.
Illustrates how tectonic landforms can arise independently of subduction.
Link to the Question:
Shows subduction is unnecessary for certain landforms, balancing the argument.

Conclusion
Subduction is crucial for forming volcanic arcs and oceanic trenches, proving its significant role in tectonic landforms at convergent boundaries.
However, mid-ocean ridges and rift valleys demonstrate that other tectonic processes, such as divergence and extension, can form significant landforms without subduction.
Judgement:
Subduction is vital for some tectonic landforms but not universally essential, highlighting a varied impact based on landform type and tectonic setting.