The mythical scenario was horrible – an earthquake in Yellowstone National Park has caused the failure of Hebgen Dam; a wall of floodwater is heading down the Madison River and will be at Ennis in little more than eight hours. Chances are Madison Dam wouldn’t be able to contain the waters coming into Ennis Lake and would also fail. Three Forks would be flooded, so would Townsend. In fact, a failure at Hebgen Dam could cause flooding in Great Falls as Canyon Ferry Dam released high flows to accommodate the influx of water from upstream. The flooding would result in thousands of evacuations, millions of dollars of property damage and widespread power outages.