= Solution
Ice accumulation adds a load that produces an immediate elastic response and slower viscous displacement of the <mantle> away from the loaded region. The depressed interior may be accompanied by a peripheral forebulge. A long-lived load approaches an approximately compensated state. Melting removes the load, giving rapid elastic recovery followed by <mantle> return flow and gradual uplift. The forebulge can subside while the formerly loaded centre rises.
\b[<Postglacial rebound> can continue long after the ice disappears], because <mantle> relaxation is slow. Raised shorelines, changing relative sea level, vertical geodetic motion and <gravity> changes record <glacial isostatic adjustment>. Present motion depends on the whole loading and melting history, <mantle> rheology and lithospheric stiffness, not only the current absence of ice.
\Image[/past-exam-of-the-physics-of-the-earth-as-a-planet-course-of-the-university-of-cambridge/2014/paper-1-pep-glacial-rebound.png]
{title=Ice loading, mantle displacement and continuing rebound after melting; schematic stages}
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