The viscosity of the asthenosphere under the continental high latitudes can be estimated from the rebound of the Earth's surface following deglaciation. This map shows the current rate of uplift across Scandanavia. The area was most recently covered in thick ice cap about 12 thousand years ago. The load from the ice cap depressed the lithosphere beneath it, displacing asthenosphere to the sides. After the ice cap melted the asthenosphere has flowed slowly back. You can continue the story by clicking here.
What are plates?