DYNAMIC INTEGRATION OF GEOTHERMAL DATA: AN EXAMPLE FROM PILGRIM HOT SPRINGS, ALASKA

Alaska has 48 hot springs (>50°C) and 49 warm to cool thermal springs (<50°C). Pilgrim Hot Springs (PHS) is one of the hottest geothermal systems in the north-central geothermal belt, extending eastward from the Seward Peninsula to the Canada border and containing 39 thermal springs related to radioactive mineral decay in plutons and extensional tectonic forces. PHS lies within the Pilgrim River valley on the Seward Peninsula, a cold climate region with discontinuous permafrost. The hot springs at Pilgrim have created a large area (~2 km²) without permafrost.

Data from PHS research is included in the Alaska Geothermal Database that is part of the National Geothermal Data System. PHS data includes remote sensing, airborne geophysics, ground-based geophysics and borehole data. The hottest temperature recorded to date is just over 91˚C with a shallow hot aquifer beneath a clay cap between 7.5 and 15 m below the surface. Below the shallow hot water is a temperature reversal into a cooler aquifer of approximately 65˚C, below which is a strong temperature gradient with a maximum temperature near bedrock of 91˚C.

Attempts to locate the upflow zone at PHS have failed. Temperature data analysis suggests an upflow zone outside the current focus area where access is difficult due to logistical obstacles. This location does not satisfy a hydrologic model that suggests that the cold aquifer is actively cooling the system and flowing past the upflow zone from the Kigluaik Mountains to the Pilgrim River. This leaves only a very small upflow region between existing boreholes where the hot water can flow from bedrock to the surface. Recently collected magnetotelluric (MT) data shed some light on the geologic structures of the sedimentary basin, but this dataset does not capture all the nuances of the flow pattern that developed over centuries. Utilizing the geothermal database, we can integrate the MT data with the geochemistry, borehole and hydrologic data to locate the actual upflow zone. This will be accomplished by 3-Dimensional geospatial referencing of this data to identify the next step in the exploration process. The Alaska geothermal database points out the shortcomings of available data for PHS as well. Adding a seismic study of PHS will identify the local fault structures to accurately locate a production well in the upwelling zone.