A NOVEL UNDERSTANDING OF THE BANFF HOT SPRINGS VIEWED AS A KARST SYSTEM

The Sulphur Mountain thermal springs (Banff Hot Springs) are the historical focal point of Banff National Park. These carbonate springs lie within a 10 km section of the 250 km long Sulphur Mountain Thrust (SMT) where it meets the topographically low-lying Bow Valley. The maximum depth of flow for the thermal water has been calculated to be around 3.2 km with discharge temperatures up to 67^oC. As the SMT contacts parallel formations of carbonate rocks along its length, it is viewed here as a hypogene karst system and some local examples of conduits that may lie within the flow system are given. The karst perspective has led to conclusions quite different from accepted wisdom. For example, several river systems cross the SMT at higher elevations, thus providing possible recharge points up to 100 km away, rather than <5km as previously thought. Furthermore, based on the apparent ¹⁴C ages of modern tufa, the distal groundwater appears be old, of thousands of years rather than seasonal. Furthermore, radiocarbon dated tufa at the springs indicates that these deposits ceased growing 3,200 years ago. This has commonly been thought to be due to climate change over the Holocene, but we suggest that postglacial karstification of the system, which dilutes the thermally supersaturated groundwater, is the principal cause. This explanation may well apply to cessation of tufa growth in glacial karst systems world-wide. In respect of ancestral drainage, we have applied glacial incision rates to the down-cutting of the Bow Valley, which yields a range of spring ages on the mountain dating from 60 ka to the present day.