资源环境科技发展态势分析平台

Researchers have long noted the potential for shallow hydrothermal fluids to perturb near-surface temperatures. Several investigators have made qualitative or semiquantitative use of elevated surface temperatures; for example, in snowfall calorimetry, or for tracing subsurface flow paths. However, a quantitative framework connecting surface temperature observations with conditions in the subsurface is currently lacking. Here, we model an area of shallow subsurface flow at Burgdorf Hot Springs, a rustic commercial resort in the Payette National Forest, north of McCall, ID, USA. We calibrate the model using shallow (0.2 m depth) ground temperature measurements and overburden thickness estimates from seismic refraction studies. The calibrated model predicts negligible loss of heat energy from the laterally migrating fluids at the Burgdorf site, in spite of the fact that thermal anomalies are observed in the unconsolidated near-surface alluvium. Although elevated near-surface ground temperatures are commonly assumed to result from locally high heat flux, this conflicts with the small apparent heat loss during lateral flow inferred at the Burgdorf site. We hypothesize an alternative explanation for near-surface temperature anomalies that is only weakly dependent on heat flux, and more strongly controlled by the Biot number, a dimensionless parameter that compares the rate at which convection carries heat away from the land surface to the rate at which it is supplied by conduction to the interface.

Plain Language Summary We studied the way in which the temperatures at the land surface vary as a result of hydrothermal fluids migrating in the shallow subsurface. Our investigation was carried out at Burgdorf Hot Springs, a rustic resort about 50 km north of McCall, ID, USA. Our results indicate that shallow hydrothermal groundwater can heat near-surface soils to readily detectable levels, and these temperatures can be used to estimate heat transfer parameters and infer conditions in the hydrothermal fluids. Our findings may make it easier and cheaper to prospect for geothermal systems and interpret surface measurements made in geothermal areas. In addition, our model suggests that elevated land-surface temperatures may be the result of factors other than those usually assumed by researchers.