Montana Earth Science Picture of the Week

Canyon Ferry Dam on the Missouri River

This picture shows Canyon Ferry Dam and Reservoir, 13 miles northeast of Helena. The dam was built on the Missouri River between 1949 and 1954 by the Bureau of Reclamation. Like other dams in Montana, Canyon Ferry serves several purposes, including power generation, flood control, recreation, and irrigation.

Your dam wind . . .
One interesting aspect of the dam is a daily wind situation that exists here in the summer. According to a colleague of mine who used to do a lot of wind surfing, a significant wind develops by the middle of sunny summer days in the area between the dam and Cemetery Island. The wind, which blows from the dam to the island, is most likely caused by the fact that land heats up faster than water. As the morning sun shines on the area, the island warms up faster than the surrounding water. By mid-day this hotter air above the island begins to rise. Watch the Convection Video (2.5 minutes). This convection causes an area of low pressure to form over the island. A fairly strong wind begins to blow from the dam as cooler air from below the dam moves to replace air rising from the island.

The big pipe . . .
Canyon Ferry Reservoir provides water used to irrigate farmland in the Helena Valley and also provides some water for municipal use in the city of Helena. Water enters the large pipe shown in the photo. A closer view of the pipe is shown in the photo below. A pump pushes the water up through the pipe, which runs underground to a storage reservoir 7 miles west of the dam. From there a system of canals deliver the water to various parts of the valley for irrigation.

Electricity . . .
Water flows through openings in the dam, drops through large tubes called "penstocks", and turns fan-like devices called �turbines�. The turbines move huge magnets located near wires, causing electricity to be generated in the wires. The device designed to convert the motion into electricity is called a generator.

Term: convection


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By Rod Benson
Earth Science Teacher at Helena High School

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