Drones spot hidden fires smoldering under Scottish mountains

When a fire burns in the wilderness, you might think the danger ends when the visible flames disappear. But beneath the ground, an invisible danger can still lurk for weeks. This is exactly what happened after a massive wildfire swept through the Cairngorms in Scotland last July.

The Cairngorms is a mountain range in northern Scotland, famous for its dramatic landscapes and wild beauty. In July, a huge wildfire destroyed thousands of acres there. Firefighters worked hard to control the flames, and eventually, the visible fire died down. People hoped the crisis was over. But scientists knew better.

Underground fires are real and persistent. Peat—a dark, rich soil made from ancient plants—covers much of the Cairngorms. When peat burns, it often continues smoldering beneath the surface for a very long time. These hidden fires are dangerous because they can suddenly reignite, spread to new areas, or harm wildlife and water supplies. The problem is simple: you cannot see these fires, so you cannot easily find them.

That is where thermal drones come in. These are not ordinary cameras. Thermal drones detect heat instead of light. They fly over burned areas and capture images that show where the ground is still hot. Warmer areas appear bright on the screen, while cooler areas look dark. Scientists can then identify exactly where underground fires are still burning—information that would be impossible to gather on foot.

The work sounds like science fiction, but it is practical and necessary. After the July fire, researchers deployed thermal drones over the Cairngorms to map all the hot spots. The drones revealed that even though the landscape looked calm and dark from ground level, numerous areas beneath the soil were still extremely hot. This data helped firefighters and environmental teams decide where to focus their efforts. They could then use water and other methods to cool the most dangerous zones and prevent new fires from erupting.

Peat fires are becoming more common. Climate change means hotter, drier conditions—perfect for fire to start and spread. Places like Scotland are learning that fighting wildfire is not just about the dramatic moment when flames rage across the hillside. It is also about the patient, invisible work of hunting down and stopping the fires that hide underground long after the smoke clears.

The next time you hear about a wildfire being "under control," you might wonder: what is still burning that we cannot see? In the Cairngorms, thermal drones now have the answer.

Inspired by reporting from BBC News.