Lakes form from a variety of sources. The formation of a natural lake will often take thousands, if not millions of years and is dependent on powerful forces within nature. The birth of a lake is often the bi-product of significant geological changes in the region. Thus, lakes of similar origin are often clustered in regions of similar geography.
Glaciers are responsible for the single largest lake in North America and the world. Lake Michigan-Huron is referred to as a glacial lake, due to the ice-filled depressions formed by receding glaciers. Although Lake Michigan-Huron are separately named, limnologists refer to these two lakes as one single system, thus technically making them the largest in the world; however, Lake Superior is the largest singly named lake in North America.
These massive glaciations occur throughout North America with the world’s highest concentration of lakes located in northeastern Canada. Massive glaciations in this region stripped the soil from the land and deposited ice in randomly-formed low points. This greatly affected the drainage system in the area, giving the region a uniquely chaotic appearance.
Drainage systems are an important part of the development of one the most common lakes, the Oxbow. Drainage systems in a region define the pattern in which rivers and streams come together. The dendritic or “tree” drainage system is the most common, known for resembling a tree when viewed from above. When sharp curves in the drainage system wear down the far shore, a slow-flowing, bow-shaped bulge can occur in the river. The Reelfoot Lake in West Tennessee formed due to as sudden change of course in the Mississippi River during the New Madrid Earthquake of 1811-1812. The name “Oxbow” is derived from that characteristic shape.
Earthquakes and volcanic eruptions are perhaps the only rapid ways for a lake to form. Lake Superior is actually referred to as a rift lake, since it is located on a fault in the tectonic plates. These lakes are typically deeper than most. Crater lakes are often formed in calderas of inactive or relatively inactive volcanoes. Mount Katmai in Alaska is one of the few true crater lakes in the United States. It is fed by glaciers that surround the lake and sits at an elevation of over 4,200 feet.
In very few instances in North America, a lake is classified as endorheic. These lakes are characterized by having no inflow and no outflow. The most prominent example of such a lake is the Great Salt Lake in Utah. Also called saline, these lakes only gain and lose water through underground sources and evaporation. As a result, endorheic lakes end up with a higher salt ratio than most inland bodies of water.
Man made lakes are often the result of the damming of flowing waterways. These lakes can vary widely depending on the application. Lake Mead is formed by the Hoover dam, and holds over 28.5 million acre feet of water – enough to cover the entire state of Pennsylvania in one-foot deep water. Landscaping projects can produce artificially fed lakes, though these lakes often fail to recycle nutrients, causing their fish populations to die annually.