Definition of asthenosphere in US English:



  • The upper layer of the earth's mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur.

    • ‘Currents beneath the plates move the plates in different directions and driving all this is radioactivity deep in the earth's mantle which keeps the under layer - the asthenosphere - molten.’
    • ‘Across the ridge, the asymmetric flow pattern in the asthenosphere will cause differential drag at the base of the lithosphere.’
    • ‘The models consist of a two-layered brittle-ductile system representing the overriding continental lithosphere, overlying a low-viscosity layer simulating the asthenosphere to provide isostatic support.’
    • ‘For one, it softens mantle rocks, thereby preparing the way for an asthenosphere - the soft layer underlying the plates.’
    • ‘Magmas erupted in continental volcanic arcs typically contain components from many sources in the crust, lithospheric mantle and asthenosphere.’
    • ‘Because the radioactive source of heat is deep within the mantle, the fluid asthenosphere circulates as convection currents underneath the solid lithosphere.’
    • ‘Scientists believe that below the lithosphere is a relatively narrow, mobile zone in the mantle called the asthenosphere.’
    • ‘Magma from the asthenosphere rises up in the form of volcanos.’
    • ‘Because the downgoing slab of lithosphere is heavier than the plastic asthenosphere below, it tends to sink passively; and the older the lithosphere, the steeper the dip.’


Early 20th century: from Greek asthenēs ‘weak’ + sphere.