Rock erosion during cold climates of the next 1 million years: risk assessment for siting a UK Geological Disposal Facility.

This project will provide unique data and understanding for sites identified by community partners as a potential UK Geological Disposal Facility (GDF) for nuclear waste. A UK GDF will be located in bedrock at depths up to a 1000 m, but the access infrastructure that will be backfilled will extend to the surface; therefore, the impacts of erosion down to 1000 m depths must be considered for each UK GDF site. Rock surface erosion (i.e. denudation) relates to all of the geological processes that work to reduce the Earth's surface, both in terms of elevation and relief. The UK is tectonically stable (i.e. non- orogenic environment) where chemical weathering and subsequent erosion accounts for much of the rock erosion; thus, this study will focus upon quantifying erosion rates as indicators of denudation.
It will adopt the following objectives:
(1) quantifying long-term erosion rates for targeted rock-types of potential UK GDFs;
(2) resolving erosion rates for past cold climates of the UK;
(3) creating a "look-up table" of erosion potential for site-specific rock-types and climate conditions over the next 1 million years.
The project will use a new, state-of-the art luminescence erosion-meter (Smedley et al. 2021) to derive rock surface erosion rates on unprecedented length and time scales. The technique works on the principle that the luminescence signal with depth into a rock surface resets to greater depths during longer exposure to sunlight over time, which can be measured. Erosion works to reduce the depth of that signal resetting, bringing it closer to the rock surface with higher erosion. Thus, for rock surfaces of known-age (e.g., existing cosmogenic nuclide dating), we can derive time-averaged erosion rates. The project will also apply state-of-the-art quantitative electron microscopy to measure the geochemistry and crystallography of rock samples and determine the chemical, physical and mechanical properties that control the rock response to erosion, and complement luminescence data (e.g., Prior, Mariani et al., 2009, Mariani et al., 2006). Rock samples for testing and analyses will be collected from locations identified by community partners to potentially host the UK GDF (e.g., Cumbria, Lincolnshire), and will be assessed for their different contexts: host bedrock (Objective 1), cold climate conditions (Objective 2).
Objective 1: The host rock environment can control the erosion rates of rock surfaces (e.g., Hall et al. 2012). However, the importance of this control is often hidden because data is compiled from a wide variety of climate zones, i.e., the environmental variables mask any impact of the rock-type (e.g., Shaw et al. 2012). Rock-type will have a significant impact upon rock surface erosion in the UK over the next 1 million years. Given that the UK (and the sites currently identified by community partners for a GDF) has highly variable local rock-types with lower to higher strengths, it is vital to quantify the potential erosion rates of the geology that hosts a UK GDF site. This project will use the new luminescence erosion-meter to quantify long-term erosion rates for a variety of lower and higher strength host rock environments targeted for any UK GDF, in combination with detailed geochemical and structural analyses.
Objective 2: There is currently no record of rock erosion rates in the UK over the glacial- interglacial cycles of the last 1 million years; thus, it is impossible to know how much erosion can be expected over the next 1 million years. A global study of rock outcrop erosion rates from across different climate variables (but not the UK) recorded a maximum erosion rate of 140 m/Ma (Portenga and Bierman, 2011) where climate parameters could explain some of the variability. Although the UK may be a non-orogenic environment considered to have low erosion rates, the combined impact of environmental variables (especially cold temperatures and high precipitation) and host rock properties