A hard surface crust is formed by solutions of minerals moving up through soil and evaporating at the surface.

The glare was frightful and soon the snow began to soften and the going became harder as our boots broke through the surface crust.

These surface features are due to the movement of very fluid lava under a congealing surface crust.

Among them, they possessed sufficient megatonnage to remove the entire surface crust of the planet.

The water ice came from 1 meter below the surface crust (the devolatized layer around the nucleus).

Thus, Mars seems to have a dynamic process of recycling of its near surface crust of carbon dioxide.

These form as a result of the continuing movement of lava below a surface crust.

The surface crust appeared as blue, shading into yellow and orange at the greater depths.

Evidently we were very far beneath the surface crust of Mars.

Inside the cup is a mantle of molten rock, covered by a surface crust not unlike our original world.