2018 Francis Birch Lecture

Abstract

The importance of Earth’s deep interior to surface processes has been obvious for some time and in different forms the subject of past Birch lectures. Elucidating the control Earth’s interior exerts on the surface can be considered one of the ultimate goals of our section and the mission that brings together many of the disciplines that constitute it and those closely related from seismology to mineral physics and geodesy. Indeed, with the advent of seismic tomography and the expanding measurements of mantle physical properties at extreme conditions we have increased our knowledge of mantle structure profoundly. Coupled with advances in geodesy and measurements of the gravity field the mantle flow we want to understand produces signals that we can observe and interpret. In the last two decades the mantle-surface interaction has been studied in unprecedented depth and illuminated with great clarity: from mantle flow exerting shear tractions that explain plate motions past and present to the origin and evolution of large-scale topography which results from normal tractions deflecting the surface. Vertical motions supported by the mantle explain much of sea-level change and continental flooding since the Cretaceous and have transformed our interpretation of sediment deposition and sedimentary basin history. Horizontal and vertical motions of the mantle are also key to the state of stress of the lithosphere and all that implies for deformation and hazards. I will review my own efforts and those of the community to bring together disparate strands of geophysics and geology to show that it is in fact impossible to understand the surface today and in the past without understanding the mantle. Put another way- the lithosphere and the mantle are not only inextricably linked but impossible to decouple.