GEOPHYSICAL AND GEOCHEMICAL CONSTRAINTS ON A REGIONAL HYDROGEOLOGICAL MODEL OF THE BANFF HOT SPRING SYSTEM, CANADA

In Banff National Park, located within the Front Ranges of the Canadian Rockies, eight thermal springs occur in a linear trend along the Sulphur Mountain Thrust (SMT) fault. In recent years the highest elevation hot springs have experienced perennial flow stoppages over the late winter to spring months, threatening critical habitat zones and causing operational interruption to a spring fed swimming pool, which is a major tourist attraction for the region. Geophysical and geochemical investigations provide spatial and temporal constraints for regional scale hydrological models of the hot spring system. Subsequent spring discharge forecasts aid in understanding the ecological threat and limiting flow disruption to the pool.

Previous studies show that spring flow is driven by precipitation infiltrating the flanks of Mount Rundle to the east, and Sulphur Mountain to the west of the SMT. Fresh water melt infiltrating Sulphur Mountain flows down through the shale-bearing units dissolving anhydrite minerals along its path and enriching the water in sulphate. Water infiltrating the flanks of Mount Rundle flows down to a maximum depth of 3.2 km where it intercepts the permeable SMT fault zone. Along this flow path the water is heated by Earth’s natural geothermal gradient and interacts with the host carbonate rock causing the water to become rich in calcium and bicarbonate. Once the water has intercepted the fault zone at depth it flows up the fault zone, mixes with cold fresh water from Sulphur Mountain and discharges from the hot springs.

Seasonal changes in the ratio of bicarbonate to sulphate concentrations suggest that the contribution of deep thermal water to shallow cold-water changes throughout the year. Furthermore, a positive correlation between spring water temperature, electrical conductivity and flow rate throughout an annual cycle suggests that snowmelt drives deep thermal water out from the reservoir connected to the springs, rather than the seasonal melt water being routed into the springs. Reduced freshwater contributions from seasonal snow melt are considered the main cause of spring flow stoppages.

Electrical resistivity and surveys transecting the SMT show a 100 m wide low resistivity zone (10 – 100’s Ωm) with a strike of approximately 300 degrees. We interpret this zone as water-bearing fractured rock of the SMT fault block. The location and orientation of the fault block agrees with regional geological maps and the location of the hot springs coincides with the western edge of the imaged fault block.