Suppose that dated raised beaches around the centre of a large former ice sheet fit…

PHYSICS · Multi-part · Fermi University Physics · Earth, Climate & Energy Physics · Seismology, tectonics and geodynamics · Seismology, tectonics and geodynamics

The Solid Earth, Ch Plates, creep and convection: the mantle in motion

Problem

Suppose that dated raised beaches around the centre of a large former ice sheet fit an exponential return with a relaxation time τr=5.0 kyr\tau_r = 5.0\,\mathrm{kyr}, and that the load had a wavelength λ=5000 km\lambda = 5000\,\mathrm{km}. Treat the mantle as a uniform viscous half-space with ρm=3300 kg m−3\rho_m = 3300\,\mathrm{kg\,m^{-3}} and g=10 m s−2g = 10\,\mathrm{m\,s^{-2}}, and take 1 yr=3.156×107 s1\,\mathrm{yr} = 3.156\times10^{7}\,\mathrm{s}. ((a)) Find the mantle viscosity ηv\eta_v this relaxation time implies. ((b)) Find the relaxation time that ηv=1.0×1021 Pa s\eta_v = 1.0\times10^{21}\,\mathrm{Pa\,s}, the Fennoscandian value, would give at this wavelength, and say what the difference suggests about the mantle this broader load samples.

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