The asthenosphere is one of the layers of earth lying below the lithosphere, approximately 80 to 200km beneath the earth’s surface and is a part of the upper mantle. It is made up of a layer of solid rocks. It has so much of pressure and heat that these solid rocks just flow down like liquids. These asthenosphere rocks are less dense than the lithosphere. This factor accounts for the movement of tectonic plates in the lithosphere to move on the earth’s surface.
The temperature defines the thickness of the asthenosphere layer. As the temperature increases, the pressure exerted also increases and the materials present in there also tend to melt and flow down. They are also involved in isostatic adjustments. The behavior of the lithosphere-asthenosphere boundary is based on the isotherm. If it is above 1300°C isotherm then it behaves rigidly and if it below it shows ductile behavior.
The hierarchy of Earth’s layers are as follows:-
|Inner core||5,000 to 6,000|
|Outer core||3,000 to 5,000|
|Mantle or Mesosphere||600 to 3000|
|Asthenosphere||100 to 250|
|Lithosphere||Up to 50|
Some extraordinary facts about Asthenosphere are
- The temperature of the Earth layers varies, so as the asthenosphere has higher temperature it always has its substances in a molten state.
- The pressure exerted is directly proportional to the temperature, so as the pressure increases the melting point also increases. In such cases, as the pressure reaches its melting point the molten asthenospheric matter bursts out through the lithosphere and floats on the earth’s surface. This molten material emerges on the earth’s surface as magma or lava from the volcanos.
- As the seismic waves move through this layer it is proved to have low velocity.
- The movement of tectonic plates causes a reduction in the pressure thus not allowing the molten substances of the asthenosphere to escape.