Influence of terrain on bedrock temperatures

Abstract

Changing terrain and underground water flows can produce anomalous underground temperatures similar to those expected from climatic changes. They can also modify the anomalies produced by past climatic changes. If these effects or their causes are not recognized, incorrect past climatic changes may be inferred from the subsurface temperatures. Three examples of terrain effects are presented and analysed: a warm lake, representing spatial differences in terrain; a deforested region, representing a temporal change in terrain; and small water flows, representing an indirect effect of terrain. There is a better chance of recognizing small anomalies due to terrain by using very accurately measured temperatures and a good representation of the thermal conductivity of the rock. Repeat temperature logs of the same hole and/or more holes in the same region also improve the detection of these effects, especially those caused by small, variable water flows. The relation of ground temperature to air temperature is a function of terrain. At two of these locations the effects of snow and surface water (shallow lakes, swampy areas) on average ground temperatures are large. Consequently climatic changes affecting either the average snow cover or precipitation and drainage at these sites would also change the average ground surface temperature even if the average air temperature remained constant. Similarly, deforestation produces directly a large warming of the ground surface (up to 4 K).