Postglacial rebound

Remarks

For a Newtonian viscous half-space of viscosity $\mu$ and density $\rho$ under gravity $g$, a depression of the form $w = w_0 \cos(2\pi x/\lambda)$ decays, by Stokes flow, as $$w(x, t) = w_0 \cos(2\pi x/\lambda) \, e^{-t/\tau}, \qquad \tau = \frac{4\pi \mu}{\rho g \lambda}.$$ Example: $\mu = 10^{21}$ Pa s, $\rho = 3300$ kg/m³, $g = 10$ m/s² and $\lambda = 3000$ km give $\tau \approx 1.3 \times 10^{11}$ s, about $4000$ years. Non-example: the immediate elastic uplift when the load is removed is not rebound in this sense; it happens at once and does not involve mantle flow. Wider loads relax faster in this model, since $\tau$ decreases with $\lambda$.