The location of abandoned mine workings using thermal techniques

Abstract

Between 1926 and 1956, laboratory experiments and underground observations demonstrated the relationship between barometric pressure decrease and the efflux gas in mines. This resulted in the establishment of early warning systems in some British mines when significant falls of atmospheric pressure were expected. In 1993, ‘frost circles’ were observed on the ground surface, above abandoned mine shafts. These were caused by warmer mine air escaping into the atmosphere, via the mine shafts. The temperature of the ground above, and in the vicinity of, abandoned mines was subsequently monitored using digital thermometers, a precision radiation thermometer and infrared thermal photography. This was followed by the use of a longer-term, ground temperature monitoring technique, using digital temperature recorders, which monitored the ground temperature every 2.5 minutes for a period of 14 days. The ground temperatures above the abandoned mine shafts were also found to be related to fluctuations in barometric pressure, agreeing with the earlier observations. During periods of high barometric pressure mine gases were prevented from escaping into the atmosphere and accumulated in the mine voids. Following a drop in barometric pressure the mine gases were capable of escaping into the atmosphere, where they underwent oxidation. This produced an increase in ground temperature in the order of a few degrees centigrade. The temperature differential may be sufficient to be detected by remote thermal imaging techniques, provided that they are undertaken in suitable climatic conditions. This type of remote, reconnaissance technique, is particularly applicable to the British Isles due to the abundance of abandoned mines workings and the regular fluctuations in climatic conditions.