asthenosfääri

The asthenosphere is a highly viscous, mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, which is the rigid outer part of the Earth, consisting of the crust and upper mantle. The asthenosphere extends from the base of the lithosphere down to a depth of approximately 700 kilometers. Its presence is crucial for plate tectonics, as it allows the rigid lithospheric plates to move over it.

The asthenosphere is not a liquid, but rather a solid that behaves plastically due to high temperatures and pressures. While it is solid rock, the conditions within the asthenosphere allow it to deform slowly and flow over geological timescales. This flow is driven by convection currents within the mantle, which in turn are influenced by heat from the Earth's core. These convective movements are the primary force behind the movement of tectonic plates.

The boundary between the lithosphere and the asthenosphere is defined by a significant change in mechanical properties. The lithosphere is rigid and brittle, breaking when subjected to stress, whereas the asthenosphere is ductile and can flow. This difference in behavior allows the lithospheric plates to "float" and glide upon the asthenosphere. Melting in the asthenosphere, though generally limited, can occur in certain regions, such as at mid-ocean ridges and above subduction zones, contributing to volcanism. The study of the asthenosphere is vital for understanding Earth's geological processes.