Medicine Lake is not actually a lake but rather an area in which the Maligne River at times backs up as it disappears into an underground cave system. During the Spring and Summer months meltwater from the glaciers on the mountains above flows into this area at a greater rate than the underground drainage system can carry it away. The river then backs up and fills this basin, like a bathtub when the faucet is flowing faster than the drain’s ability to carry the water away. During the winter the amount of water flowing into the lake decreases to the point that the drainage capacity can easily take more water than is flowing in and the lake disappears and becomes a river flowing through the empty ‘lakebed’. Using the example of the bathtub, the faucet is now only running a trickle, and the water level in the tub falls. Only during years of exceptional melt does any water drain overland from here. That area can be seen from the old parking lot at N 52° 52.186 W 117° 48.377. The underground passageways that drain Medicine Lake are one of the largest underground river systems in the world. They flow through what is known as the Maligne karst system, a network of caves through limestone of the Upper Devonian Palliser Formation. Depending on the time of year, tracer dyes placed in the water take from half a day to a week to travel the ten miles downstream to the Maligne Canyon. The dyes though do not just come out at the canyon, but also well up in many of the lakes lower down the valley, as far away as Lac Beauvert and the Athabasca River. All of this is made possible by the presence of karst. Karst is a landscape formed from the dissolution of soluble rocks including limestone, dolomite and gypsum. It is characterized by sinkholes, caves, and underground drainage systems. Nearly all surface karst features are formed by internal drainage, subsidence, and collapse triggered by the development of underlying caves. Rainwater becomes acidic as it comes in contact with carbon dioxide in the atmosphere and the soil. As it drains into fractures in the rock, this acidic water begins to dissolve away the alkali rock creating a network of passages. Over time, water flowing through the network continues to erode and enlarge the passages; this allows the ‘plumbing system’ to transport increasingly larger amounts of water. In order to log this cache please email the cache owner the answers to the following questions, and post a photo of yourself with your GPSr and the ‘lake’ in the background. All the answers can be found on the signs in the parking area. The questions were modified on Aug. 1, 2017 due to damage to one of the signs.
1. To where has the outflow been traced, and how far down valley is this?
2. The lake level fluctuates by up to 20 meters. What business was hampered by the fluctuating water levels on the lake? What did people do to try and stop the fluctuations?
3. Please post a photo of the lake, and if you wish put yourself in it! The photo catalogue that is created shows how amazingly the lake level changes from season to season and year to year.
Please send the answers before posting a find, or the find log will be deleted. Each cacher logging the find is responsible to post their own answers. Thanks.