Skeiðarársandur is a large area of black sands, reaching from Skeiðarárjökull (a part of Vatnajökull) to the sea.

It is a glacial outwash plain covering an area of 1300 km², formed as the Skeiðará and other glacial rivers fed by the Skeiðarárjökull glacier washed material towards the sea. The rivers carry material that surfaced during sub-glacial volcanic eruptions in Vatnajökull. There used to be little vegetation on Skeiðarársandur, but in the 21st century a self-seeded forest of birch trees has been spreading. Skeiðarársandur is a nesting area for the great skua.