Geoid height versus topography for a plume model of the Hawaiian swell

We use a three-dimensional variable-viscosity convection model of a station ary plume beneath a drifting lithosphere to study the factors that control the geoid-to-topography ratio (GTR) of the Hawaiian swell. The rate of melt ing in the plume is predicted using a batch melting parameterization, and t he melt is assumed to migrate to the surface where it builds a volcanic edi fice. equivalent to the Hawaiian island chain. Viscous stresses, elastic de formation of the lithosphere and (optionally) the volcanic material deposit ed on the ocean floor are included in the calculation of surface topography and the corresponding geoid. The derivation of the GTR from the model imit ates methods that have previously been used to estimate the 'observed' GTR for the Hawaiian swell. The first method we use here is that of Marks and S andwell [J. Geophys, Res. 96 (1991) 8045-8055], which applies bandpass filt ers to retain only wavelengths from 400 to 4000 km as most characteristic o f the swell topography and geoid, and the GTR is estimated from the slope o f the regression line of geoid versus topography. Another group of methods analyzes the data along profiles drawn across the hotspot swell and elimina tes the unwanted signals, e.g, the volcanic islands and the flexural moat a round them, by cutting out parts of the sections. The GTR is then calculate d from curves which best fit the topography and geoid profiles on the swell flanks only. In our plume model, when the effects of the volcanic surface loading are included, Marks and Sandwell's method yields 4.4 m/km for the G TR, while profile-fitting on the swell flanks gives 7-8.5 m/km. Ignoring th e volcanic load leads to 7-8 m/km in all processing methods. The observed G TR for the Hawaiian swell has been reported to lie between 4 and 5 m/km. An alysis of the data processing methods shows that the applied bandpass filte rs cannot completely remove the signal due to the volcanic edifice and lith ospheric flexure and this causes apparent GTRs around 4 m/km. The 'pure' sw ell model containing no volcanic load on the surface demonstrates that the Hawaiian swell may have a proper GTR near 7 m/km. (C) 2000 Elsevier Science B.V. All rights reserved.