What is happening between earths lithosphere and asthenosphere when they are in a state of isostasy?

The state of isostasy suggests that the Earth's lithosphere is floating over the asthenosphere. This is due to the difference in density between the crust from the lithosphere and the mantle layer, the crust is less dense than the mantle so it is floating above it at a certain elevation. This is also the reason for all of the tectonic movement and process on the Earth.

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