Model Answer
0 min readIntroduction
The Earth’s outermost shell, the lithosphere, is not a continuous entity but is fragmented into several pieces called lithospheric plates. These plates are constantly in motion, driven by forces within the Earth. The theory of plate tectonics explains the large-scale geological features and phenomena observed on Earth, including earthquakes, volcanic eruptions, and mountain building. The devastating tsunami of December 2004, triggered by a massive earthquake in the Indian Ocean, serves as a stark reminder of the power of plate tectonic processes.
What are Lithospheric Plates?
Lithospheric plates are rigid segments of the lithosphere – comprising the crust and the uppermost part of the mantle – that move and interact with each other. These plates vary in size and thickness, ranging from a few hundred to thousands of kilometers across and from 5 to 100 kilometers thick. They can be oceanic (composed primarily of dense basaltic rocks) or continental (composed primarily of less dense granitic rocks), or a combination of both.
The Theory of Plate Tectonics
The theory of plate tectonics, developed in the 1960s, revolutionized our understanding of Earth’s dynamic processes. It posits that the lithosphere is divided into these moving plates that “float” on the semi-molten asthenosphere below. The primary driving forces behind plate movement are:
- Mantle Convection: Heat from the Earth’s core causes convection currents in the mantle, dragging the plates along.
- Ridge Push: Newly formed lithosphere at mid-ocean ridges is hotter and less dense, causing it to “slide” downhill, pushing the plates away from the ridge.
- Slab Pull: As a dense oceanic plate subducts into the mantle, it pulls the rest of the plate along with it.
Types of Plate Boundaries
The interaction between plates at their boundaries results in different geological features:
- Divergent Boundaries: Plates move apart, allowing magma to rise and create new crust (e.g., Mid-Atlantic Ridge).
- Convergent Boundaries: Plates collide. This can result in:
- Oceanic-Continental Convergence: Subduction of the oceanic plate beneath the continental plate, leading to volcanic arcs and trenches (e.g., Andes Mountains).
- Oceanic-Oceanic Convergence: Subduction of one oceanic plate beneath another, forming volcanic island arcs and trenches (e.g., Mariana Islands).
- Continental-Continental Convergence: Collision and uplift, forming mountain ranges (e.g., Himalayas).
- Transform Boundaries: Plates slide past each other horizontally, causing earthquakes (e.g., San Andreas Fault).
The 2004 Indian Ocean Tsunami
The devastating tsunami of December 26, 2004, was triggered by a magnitude 9.1-9.3 earthquake off the coast of Sumatra, Indonesia. This earthquake occurred due to the subduction of the Indo-Australian Plate beneath the Eurasian Plate. Specifically, the earthquake occurred along the Sunda Trench, a subduction zone where the Indo-Australian Plate is being forced under the Eurasian Plate. The rupture zone extended for approximately 1,200 kilometers, making it one of the longest ever recorded. The sudden vertical displacement of the seafloor generated massive tsunami waves that radiated outwards, impacting coastlines across the Indian Ocean, including India, Sri Lanka, Thailand, and Somalia.
Conclusion
The theory of plate tectonics provides a unifying framework for understanding Earth’s geological processes. The 2004 Indian Ocean tsunami tragically demonstrated the immense power of these processes and the vulnerability of coastal communities. Continued research and improved early warning systems are crucial for mitigating the risks associated with plate tectonic activity and protecting lives and infrastructure. Understanding plate boundaries and their associated hazards remains paramount for effective disaster preparedness.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.