LAUSR

Deformation of the Earth in response to forcing transitions from elastic to viscous is increasing with timescale and temperature. For example, on the short timescales relevant to forcing from seismic waves and tides (seconds to days), the deformational response of the mantle is essentially elastic. Meanwhile, the solid rocks in the mantle are also warm, weak, and deform viscously in response to forcing imposed on very long geologic timescales (>10–10 years) by temperature gradients between the surface and the core-mantle boundary. In contrast, the surface thermal boundary layer (or lithosphere) is cold, very stiff, and typically behaves like an elastic plate even on the long timescales relevant to mantle convection. However, lithospheric rocks are also capable of viscous flow where they are warmed and subject to forcing on long timescales (e.g., continental rifting, magmatism, lithospheric small-scale convection). On intermediate timescales (10– 10 years), both modes of deformation are relevant to the dynamics of mantle-lithosphere systems, and such processes are fundamentally viscoelastic (e.g., subduction zone dynamics, glacial isostatic adjustment, flexure, isostasy, orogeny, and tectonics). Since such processes collectively are the manifestation of plate tectonics, it is essential to improve and expand our understanding of viscoelastic rheology in the mantle and lithosphere. In particular, the volcanic Island of Hawaii has been steadily built over the past ∼1 Myr and acts as a surface load which induces viscoelastic deformation and flexure. Observations of this deformational response to loading offer a unique opportunity to constrain the rheology of the intraplate lithosphere at the Island of Hawaii.