In geophysics, especially regarding gravimetry, the phrase load density ("the density of a load") refers to a load weighing down the lithosphere (top layer of the Earth down to somewhat below the crust). Examples of such a load are a volcano, a layer of ice (glacier), or a portion of the lithosphere pushed up on top of another a portion (plate tectonics). Something loading the lithosphere can also be within it, i.e., a highly dense volume within the lithosphere but below the surface. Models of the statics and dynamics of geological land formation may characterize such a load by a load thickness and a load density over some area. Such models relate data from gravimetry and surveys to the underlying structure.