March 26, 2013

What is a Lake?

Hi, I’m Emerald Robinson, and in this “What is?” video, we’ll tackle the question, “What is a Lake?”

A lake is a body of water that fills a depression in the earth’s crust called a basin. Lakes are usually fairly large in size, surrounded by land, and are fed and drained by a river or stream. Compared to other bodies of water like oceans and rivers, lakes are fairly calm, and have neither large waves nor strong currents.

There are millions of recognized lakes, since the definition of what a lake is varies widely and from place to place. Sometimes small lakes are called ponds, and larger ones are called seas.

At about 143,000 square miles in area, the Caspian Sea is considered to be the world’s largest lake, while the deepest lake is Russia’s Lake Baikal, which is about a mile in depth.

Lakes are formed in many different ways. Retreating and melting glaciers can leave lakes in their path. Other lakes are created by plate tectonics, or even by water filling a volcano’s crater. Humans also frequently create lakes for recreation or for hydropower by damming rivers.

Limnologists, scientists that study freshwater systems, can actually determine a lake’s age. This is because all lakes will eventually dry out as their basins fill with sediment and other natural debris. Dry lake beds are a common site in which to find fossils.

Although most lakes contain freshwater, there are some exceptions. The Great Salt Lake in the United States is what is called a “closed” lake, which means that water only leaves the lake by evaporation. The Great Salt Lake’s water is even saltier than ocean water!

The ways we can classify lakes are almost too many to count. Size, the amount of nutrients, how their water mixes – even what types of fish inhabit them, are all methods used to classify the earth’s many lakes.

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