Simon Stephenson

I am interested in understanding how processes within the Earth’s mantle are manifest at the surface in landscapes and in the geological record.  By understanding this coupling it is possible to exploit geomorphic and geological observations to constrain the elusive history of mantle convection.

Convection within the Earth’s mantle deflects the surface of the Earth, generating topography.  Hot blobs of material within the mantle rise upwards, causing topographic doming, while cold sinking slabs generate depressions.  This so-called “dynamic topography” causes uplift and subsidence of up to about 1 km over 1000 km length scales.  Hence it is a key, yet poorly-understood driver of surface processes such as fluvial erosion, sediment transport and deposition.  Importantly, mantle convection can alter the heights of sea-level markers, which affects how we interpret sea level in the geological past.

My research involves exploiting the effect that dynamic topography has on these surface observations and processes such as landscape evolution, the sedimentary record, sea-level markers, and magmatism.  I combine surface geophysical, field and laboratory constraints with seismic images of the subsurface to link the surface to the deep.

Primary Research Projects

• Constraining lithospheric structure and modern-day pattern of residual topography on the continents.
• Constraining the history of mantle-driven uplift and subsidence.
• Response of landscapes to long-wavelength uplift and climatic forcing.
• Interaction of sea level, glacial-isostatic adjustment and mantle convection.
• Constraining asthenospheric and lithospheric mantle structure with basalt geochemistry.

Project Supervision

• Subsidence of the Argentine Abyssal Plain (Cambridge).
• Cretaceous carbonate compensation depth (Oxford).
• Subduction and tectonic history of Alaska and Chukotka (Oxford).
• Residual topography of the Eastern Australian Margin (Cambridge).
• Global evolution of the Great Escarpments on passive margins (Cambridge).

Collaborators

Below is a non-exhaustive list of many of the great people that I get to work with!

• Karin Sigloch (Oxford)
• Nicky White (Cambridge)
• Mark Hoggard (Harvard)
• Patrick Ball (ANU)
• Jenny Jenkins (Durham)
• Megan Holdt (Cambridge)
• Fred Richards (Imperial)
• Fergus McNab (GFZ Potsdam)
• Gareth Roberts (Imperial)
• Ben Conway-Jones (Cambridge)
• Laura Robinson (Bristol)
• Jacky Austermann (Lamont-Doherty)
• Andy Carter (UCL)
• Diane Seward (Welington/GNS)