Beneath the oceans, the crust varies little in thickness, generally extending only to about 5 km. The thickness of the crust beneath continents is much more variable but averages about 30 km; under large mountain ranges, such as the Alps or the Sierra Nevada, however, the base of the crust can be as deep as 100 km.

What is the average depth of the crust?

Crust. The Earth's crust ranges from 5–70 kilometres (3.1–43.5 mi) in depth and is the outermost layer. The thin parts are the oceanic crust, which underlie the ocean basins (5–10 km) and are composed of dense (mafic) iron magnesium silicate igneous rocks, like basalt.

What is the thickness of the crust answer?

The average thickness of the crust is about 15 km (9 mi) to 20 km (12 mi). Because both continental and oceanic crust are less dense than the mantle below, both types of crust "float" on the mantle.