The study focuses on the assessment of surface area thermal activity measured by air thermal photography at the significant geotourism locality of Ema coal tailing dumps. Ema has become a geotourism post-mining landmark associated with black coal mining in Ostrava, the third largest city in the Czech Republic. At the same time, Ostrava is the largest industrial city in the Czech Republic. The study analyses a new approach to assess the surface area thermal activity in coal tailing dumps. A correct analysis of the surface area thermal activity is a fundamental requirement for projects to deal with the clean-up of a dump with thermal activity. Ema has a scientific and geotourism–educational character and it is important to plan solutions to achieve thermal activity stabilization. A 4 year monitoring programme was implemented using a new approach grounded in assessment based on thermal activity area classification (active and inactive), and comparison with a reference point in the dump with the highest temperature without thermal activity during the measurement period. It was this boundary condition that facilitated the correct assessment of the thermal activity surface area and it helped to establish gradual decreases in thermal activity from 0.29 ha (i.e. 0.79% of the total area of the dump) in 2011 to 0.15 ha (i.e. 0.41% of the total area of the dump) in 2014.