Responses of alluvial rivers to environmental change

Alluvial rivers are the primary way in which sediment is transported from eroding source areas to depositional sinks. They aggrade, incise and adjust their rates of sediment transport in response to changing environmental conditions. These processes can leave behind terraces along alluvial rivers and facies variations in sedimentary successions downstream. We are developing models and collecting field observations to build a coherent and quantitative understanding of this behaviour. Ultimately we hope to facilitate intepretation of these archives in terms of past environmental change. See McNab et al. (2023) for a description of our modelling results.

Depths and temperatures of mantle melting

The eruption of magma at volcanic centres is one of the clearest surface expressions of mantle convection in Earth's dynamic interior. However, many questions remain regarding how and why mantle melting occurs where and when it does. Useful information can be obtained by calculating pressures and temperatures of melting from the geochemistry of volcanic rocks. We developed a Python package, called meltPT, for the application of major-element thermobarometers and for comparison between their results and predictions of geothermal models. See McNab and Ball (2023) for an overview of the software and a case study on Hawaiʻi, and McNab et al. (2018) for an earlier application to Anatolia.

Mantle convection and Earth's surface landscape

Convection deep in the Earth's mantle causes uplift and subsidence of the surface, but its influence is often subtle and difficult to discern from that of plate tectonic processes. One way to disesntangle these effects is to analyse the shape of the landscape, which reflects the combination of uplift, subsidence, and erosion. In particular, if erosion can be parameterised, we can infer uplift-rate histories across the continents. Away from plate boundaries, these results provide direct constraints on mantle-driven uplift. Close to plate boundaries, this information can be combined with independent evidence such as the timing and composition of volcanism to distinguish between different uplift mechanisms. See McNab et al. (2018) for analysis and discussion of the development of Anatolian Plateaux.

Ancient transient landscapes

Assessing the influence of mantle convection on the Earth's surface through geologic time is challenging since its effects are generally subtle and impermanent. An exception may be in shallow water continental basins, which, in the absense of geodynamic effects, slowly subside and accumulate sediment. If such basins are subjected to a phase of mantle driven uplift, they can become exposed, trigerring a phase of fluvial incision. On the resumption of steady subsidence, fluvial valleys are infilled and the transient landscape preserved, along with information about the amplitude and rate of uplift. Ancient landscapes can therefore provide rare insights into patterns of mantle convection in deep time. See McNab and White (2022) for discussion of such a landscape exposed in the Grand Canyon, USA.