Figure 1

The site of underground combustion of brown coal studied in the work. (A) Location map. The red rectangle shows the location of the study area. The map was derived from a United Nations map (https://commons.wikimedia.org/wiki/File:Un-russia.png) which is in the public domain. (B) General view of the area where coal combustion occurs. The bottom part shows the fumarole-like structures. The images were taken by the authors.