Thermal anomalies are phenomena of unexpected thermal behaviour, caused by thermal effects unknown in the first instance. In land and water bodies these may origin, for example, from gases emerging from deep reservoirs or from springs, submerged in water bodies. Their surface thermal impact is superimposed to the environmental thermal impact and dampens the changes induced by the latter. The method of minimal thermal change detection utilizes this effect to identify and investigate such events. It applies repeated acquisition of congruent infrared images of areas of interest under changing thermal environment. From these images, regions of low thermal change are identified. Application to natural CO2 vents resulted in their reliable localization. Tools for the measurement of vent gas flux and temperatures were developed and successfully applied.