Asthenosphere

Definition

The asthenosphere is a semi-fluid layer of the Earth's mantle located beneath the lithosphere, playing a critical role in plate tectonics. This layer, characterized by its ability to flow slowly, allows the rigid lithospheric plates to move over it, enabling processes like isostasy, crustal thickening, and the formation of continents and ocean basins.

5 Must Know Facts For Your Next Test

1. The asthenosphere extends from about 100 km to 700 km beneath the Earth's surface and has a temperature range of approximately 1,300°C to 2,000°C.
2. Its semi-fluid properties are due to partial melting and high temperatures that enable it to deform and flow over geological time scales.
3. The movement of tectonic plates over the asthenosphere is driven by mechanisms such as mantle convection, ridge push, and slab pull forces.
4. The asthenosphere is crucial for processes like isostatic adjustment, which occurs when weight is added or removed from the Earth's surface, affecting how the lithosphere behaves.
5. Changes in the asthenosphere can influence volcanic activity and seismic events by altering how stress is distributed across tectonic plates.

Review Questions

• How does the asthenosphere contribute to the movement of tectonic plates?
  • The asthenosphere's semi-fluid nature allows it to act as a lubricant for tectonic plates that rest on top of it. This movement is facilitated by convection currents within the mantle, which create forces such as ridge push and slab pull. These forces help drive plate motions as they interact with the more rigid lithosphere above. Consequently, understanding the asthenosphere's role is essential to grasping how tectonic activity occurs across Earth.
• In what ways does isostasy relate to the behavior of the asthenosphere?
  • Isostasy refers to how different parts of the Earth's crust balance on top of the denser mantle below. The asthenosphere plays a crucial role in this process as it allows for vertical movements and adjustments of the lithosphere based on changes in weight from surface features like mountains or glaciers. When there are shifts in mass on the surface, such as erosion or sediment deposition, the lithosphere can sink or rise with respect to the asthenosphere to maintain equilibrium.
• Evaluate how changes in the asthenosphere could impact volcanic activity and seismic events globally.
  • Changes in the asthenosphere can significantly influence volcanic activity and seismicity by altering stress distribution within tectonic plates. For example, if the asthenosphere becomes more fluid due to increased heat from below, it can lead to reduced friction along plate boundaries, potentially causing more frequent volcanic eruptions and earthquakes. Conversely, if cooling occurs and makes the asthenosphere less mobile, it could lead to plate stagnation and fewer geological disturbances. Understanding these dynamics helps geologists predict potential hazards linked to volcanic eruptions and earthquakes worldwide.

Related terms

Lithosphere: The rigid outer layer of the Earth, consisting of the crust and the uppermost part of the mantle, which is broken into tectonic plates.

Mantle Convection: The process by which heat from the Earth's interior causes the slow movement of material in the mantle, driving the motion of tectonic plates.

Isostasy: The equilibrium between the Earth's crust and the mantle, where the lithosphere 'floats' on the more fluid asthenosphere, adjusting to changes in surface load.