A Reconnaissance Study of the Hydrothermal Characteristics of Pilgrim Springs, Alaska

Abstract

A reconnaissance level study of the Pilgrim Springs geothermal system was conducted to determine the near-surface thermal regime and to obtain information on the ground water flow regime within the thawed ground area. Measurements included soil temperatures, apparent electrical conductivity of the soil, electrical conductivity and temperature in the Pilgrim River, saturated hydraulic conductivity of the soil and ground water flow characteristics (direction and velocity). In addition the size, number and characteristics (geometry, direction of flow) of near-surface convective plumes were investigated. Measured temperature profiles were used to estimate ground water flow velocities. There are approximately 2–3 km2 of thawed ground surrounded by permafrost on the order of 100 m in thickness. The highest temperatures were found in the southwest quadrant of the thawed area where a pool of ground water at ≈ 92°C exists at 14–32 m below the ground surface. Temperature measurements suggest that water in the pool is flowing laterally and vertically. Temperature and electrical conductivity measurements suggest that this pool of water underlies most of the thawed ground area although the possibility of several, unconnected sources of hot water and multiple pools has not been ruled out. Conductivity measurements suggest that hot and/or saline water rises in convective plumes from the pool at about 40–60 sites. The Pilgrim River appears to be heated by heat transfer from the geothermal area. Saline ground water enters the Pilgrim River, probably through its bed, increasing the conductivity of the river water.