Model Answer
0 min readIntroduction
Sea-floor spreading is a crucial process in plate tectonics, responsible for the formation of new oceanic crust. It occurs at divergent plate boundaries where tectonic plates are moving apart. This process, first proposed by Harry Hess in the 1960s, fundamentally changed our understanding of Earth’s dynamic surface. The upwelling of magma from the mantle to fill the gap created by the separating plates not only creates new crust but also fuels significant volcanic activity along these boundaries, shaping the geological landscape of our planet.
Mechanism of Sea-Floor Spreading
Sea-floor spreading is driven by convection currents within the Earth’s mantle. These currents are caused by heat from the Earth’s core radiating outwards. Hotter, less dense material rises, while cooler, denser material sinks. At divergent plate boundaries, this rising mantle material exerts an upward force, causing the plates to separate.
- Ridge Push: The elevated mid-ocean ridges created by the upwelling magma exert a gravitational force, pushing the plates away from the ridge.
- Slab Pull: At subduction zones, the denser oceanic lithosphere sinks into the mantle, pulling the rest of the plate along with it. While not directly part of spreading, it influences the overall plate movement.
Volcanism Associated with Sea-Floor Spreading
As plates diverge, the pressure on the underlying mantle decreases. This reduction in pressure leads to partial melting of the mantle rock, generating magma. This magma rises through fissures and cracks in the oceanic crust, erupting as lava and forming new basaltic crust. This process is the primary source of volcanism at mid-ocean ridges.
Examples of Sea-Floor Spreading and Volcanism
- Mid-Atlantic Ridge: This is a prime example of a divergent plate boundary and a site of active sea-floor spreading. Volcanic activity along the ridge has created numerous volcanic islands, such as Iceland.
- Iceland: Situated on the Mid-Atlantic Ridge, Iceland is a volcanic island formed by the continuous eruption of basaltic lava as the North American and Eurasian plates diverge. The island experiences frequent volcanic eruptions and geothermal activity.
- East Pacific Rise: Another significant example, the East Pacific Rise is characterized by faster spreading rates and more intense volcanic activity than the Mid-Atlantic Ridge.
- Red Sea: The Red Sea is a nascent ocean basin formed by the divergence of the African and Arabian plates. Volcanic activity is present, though less pronounced than at well-established mid-ocean ridges.
Types of Volcanic Activity
The volcanism associated with sea-floor spreading is predominantly effusive, meaning it involves relatively gentle outpourings of lava. This is due to the low viscosity of basaltic magma. However, explosive eruptions can occur, particularly where water interacts with the magma, creating phreatomagmatic eruptions.
| Feature | Description |
|---|---|
| Magma Type | Primarily basaltic, low viscosity |
| Eruption Style | Mostly effusive, some phreatomagmatic |
| Landforms | Mid-ocean ridges, volcanic islands, seamounts |
Conclusion
Sea-floor spreading is a fundamental geological process that drives plate tectonics and generates new oceanic crust. The associated volcanism, primarily effusive in nature, shapes the ocean floor and creates unique geological features like Iceland. Understanding this process is crucial for comprehending Earth’s dynamic nature, predicting volcanic hazards, and interpreting the geological history of our planet. Continued monitoring of mid-ocean ridges and volcanic islands provides valuable insights into these ongoing processes.
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.