Exploring Scotland’s hidden energy potential with geology and geophysics: fieldwork in the Cairngorms 

As a geologist and geophysicist, my research focuses on understanding whether Scotland’s radiothermal granites could help unlock a new source of sustainable geothermal energy for the UK. In summer 2024, I conducted a three-week field campaign to study the potential for geothermal energy in the Cairngorms with a team of other geoscientists. 

The Cairngorms: more than just mountains

Geothermal energy is often associated with places like Iceland or other volcanic hot spots, but Scotland’s ancient granites may also be able to supply sustainable heat. The Cairngorm Pluton, part of the East Grampians Batholith, is one of the UK’s highest heat-producing granites, with intriguing geothermal potential. My work combines geophysical surveying with laboratory experiments to explore this potential, whilst addressing uncertainties about the region’s geology. 

Using magnetotellurics to explore below the surface

Magnetotellurics (MT) is a deep-sounding geophysical technique that uses the Earth’s natural electromagnetic field to produce images of the conductivity properties of the rocks in the subsurface. It can also be used to map features like fluid pathways and fractures located several kilometres below the surface. These pathways are critical for geothermal energy because they act as conduits for the fluids transporting heat. 

During my fieldwork in the Cairngorms, we set up 24 MT stations using instruments on loan from the NERC Geophysical Equipment Facility across the region. These were deployed by a team comprising myself and: 

• BGS staff members 

• Heriot-Watt University staff 

• other postgraduate researchers 

• a Cairngorm ranger 

• a University of St Andrews undergraduate student 

The MT equipment uses two types of sensor:  (1) non-polarisable electrodes, which measure the ground electric field, and (2) induction coil magnetometers, which measure changes in the magnetic field. The setup at each site required us to bury the sensors to protect them from the fierce weather conditions.

The data collected from the sensors will allow us to produce images of the Earth’s electrical resistivity below the surface using a mathematical process called data inversion. Ideally, the images could show zones with lower electrical conductivity, where fractures in the rocks are present within the resistive granite. These could be potential geothermal reservoirs from which heat can be extracted.

Fieldwork challenges and discoveries

Conducting fieldwork in the beautiful but bleak Cairngorms is both rewarding and challenging. With no roads in much of the area, we had to carry our equipment, including a 20 kg battery, over many kilometres of hiking paths and sometimes beyond any trails. Navigating deep bogs, steep bouldery terrain and elevations of up to 1250 m while braving sudden weather changes was an adventure in itself. In June 2024 we had seven consecutive days of snow fall on the mountain!

In addition to the MT fieldwork, I surveyed the geological structures and outcrops and collected samples for later laboratory analysis. One memorable moment came when we discovered a zone of extensive hydrothermal alteration of the granite near Stob Coire an t-Sneachda. This is possible evidence of hot fluids chemically changing the rock many millions of years ago. This alteration is significant because it could enhance the porosity and permeability of the rock, which are crucial factors for geothermal reservoirs.

Why it matters

Geothermal energy offers a constant, low-carbon source of heat, making it a promising candidate for the UK’s renewable energy mix. Additionally, its small land footprint and minimal surface infrastructure requirements mean it can provide sustainable energy with reduced visual impact, preserving the natural landscape. My research aims to de-risk geothermal exploration in Scotland, providing the scientific basis for future projects that could benefit communities and combat climate change.

Next steps

With my first year of fieldwork complete, I’m back in the laboratory, analysing samples and processing the MT data to build a three-dimensional resistivity map of the Cairngorm Pluton. Combining geophysical models with laboratory-based analyses will bring us closer to understanding the geothermal potential of this region of Scotland.

Thanks

Thanks go to Nathaniel Forbes Inskip and Andreas Busch from Heriot-Watt University and Juliane Huebert from BGS.

All images kindly reproduced with permission. For enquiries about the images within this article, please contact the copyright team (IPR@bgs.ac.uk).