What Are Ways Lakes Are Formed?
- At the end of the last ice age, the ice sheets that covered the northern United States began to retreat to Canada, where they originated. Warming temperatures in the Northern Hemisphere essentially melted a vast majority of the sheet. When this occurred, large amounts of water were dumped into the United States and parts of southern Canada. The result was the creation of new lakes. The best-known lakes formed this way are Lake Huron, Lake Superior, Lake Erie, Lake Ontario and Lake Michigan, which are collectively known as the Great Lakes.
- Today, many lakes are formed by human activity. More often than not, man-made lakes are formed by the construction of a dam on a river. Dams block natural river flow, which in turn, causes water to build up behind it. Dams are primarily constructed in areas where large bodies of freshwater are not abundant. Dams can fight both droughts and floods.
During droughts, they provide water to thirsty lands. During floods, dams prevent water from flowing into and destroying the countryside. Well-known man-made lakes such as Lake Victoria in Africa and Lake Tahoe in the western United States also employ dams at outlet channels, the area where lakes dispel their water. These dams allow operators to control the levels of the dam's respective lake. - Lakes can also be formed in more unusual circumstances, such as the sinking of land from the interactions of tectonic plates. The most famous lake formed by this process is the Dead Sea, a salty lake in the Middle East. At this location, a rift is forming. A rift is a sunken area caused by the separation of two tectonic plates. The stresses from the two plates pulling apart thins the soil. Pressures from the land compact this thinned soil, causing it to sink. Over time, water has gathered in this area, mainly due to the contributions of the lake's only tributary, the Jordan River.
- The Caspian Sea is the lake with the largest surface area on Earth, surpassing both the Great Lakes and Lake Victoria. Like the Dead Sea, the Caspian Sea is salty. Still, it only has 10 to 13 grams of salt per liter of water. The Earth's oceans have about three times as much salt per liter as this.
At one time, the Caspian Sea was part of an ancient ocean called the Thetis Ocean. Fifty million to 60 million years ago, this body of water connected the Atlantic and Pacific oceans. Eventually, due to the movement of the Earth's plates, this connection was cut off and parts of the Thetis Ocean became completely landlocked, forming the Caspian Sea.
