Scaling the Swell: Plume‐Lithosphere Interaction and Its Signal in Dynamic Seafloor Topography

Abstract

Hotspot swells provide key constraints for understanding plume‐lithosphere interaction. However, quantitative relationships between plume properties and swell morphology remain poorly constrained. Here, we use 3D regional geodynamic models with composite diffusion‐dislocation creep rheology to investigate plume‐lithosphere interaction for intraplate hotspots. Model results show that plume material spreads beneath the lithosphere, forming a pancake that is modulated by non‐Newtonian rheology in the asthenosphere. Plume material spreads downstream notably more rapidly than plate motion, deflating the swell. Based on the modeled swell geometry, we derive two sets of empirical scaling laws linking surface dynamic topography to mantle plume properties. A simplified set relates swell height, width, and cross‐sectional area to plume buoyancy flux and plate velocity, while a second, more comprehensive set links swell geometrical metrics to plume radius, excess temperature, and plate velocity. Applying these scalings to observations for the Hawai'ian swell yields plume surface buoyancy fluxes well exceeding 4.2 Mg/s. The latter scaling yields either a narrower and hotter (297 km wide, excess temperature of 348 K) or a wider and cooler plume (447 km, 162 K), corresponding to plume surface buoyancy fluxes of 5.1 ∼ 5.6 Mg/s. Pure diffusion‐creep test models demonstrate that composite rheology systematically modifies swell geometry and its dependence on plate velocity, underscoring the relevance of our new scaling. Although melting‐related compositional buoyancy is not explicitly considered in our simplified models, these scalings provide improved quantitative links between surface dynamic topography and deep mantle plume properties.