In this lesson, you will learn how groundwater and surface water form features on Earth and cause changes in landscapes. You will also learn about the different types of features formed by each type of water.
Ground and Surface Water
Our Earth is mostly water - about 70%, in fact. Water is important on Earth not only because it supports life in a variety of ways, but it is also responsible for forming and changing much of Earth's surface. Both groundwater and surface water shape the landscape and create landforms, but they do so in different ways. In order to understand how Earth is shaped by water, we need to understand what these two types of water are.
Groundwater is water below Earth's surface, in what is called the saturated zone. The saturated zone is the region underground where water completely fills any open spaces. Water below Earth's surface also exists as soil moisture, which is found in the unsaturated zone. The unsaturated zone is located just above the saturated zone. This area is not completely saturated with water, and there's still a significant amount of air in the soil.
Surface water is what most people see as streams and rivers. Rivers are really just larger, faster-moving streams, so for simplicity, we're going to call all surface water 'streams.' Streams are dynamic systems that transport water and provide energy and nutrients through this movement.
Effects of Groundwater - Human-Influenced
Even though groundwater is moving slowly underground, it can still cause some pretty drastic changes in landscape. Some of these changes are caused by humans, but most of the time, the changes are caused because gravity causes movement of the water.
One way that humans can cause landscape changes through groundwater movement is by pumping it from the ground. Many people use wells to get the water they need for drinking, showering, and other household uses. When too much groundwater has been pumped from the ground, the land actually lowers because gravity pulls it down into the space that the groundwater occupied previously. When this happens, the land has subsided.
There are some famous examples of land subsidence, such as the Leaning Tower of Pisa. The tower was built on unstable ground, and as the ground compacted from extreme groundwater pumping, the tower began to sink with the land and then tilt. Another example of extreme land subsidence is in the San Joaquin Valley of California. Too much groundwater was pumped for agricultural irrigation and the land surface sank down about 27 feet. Even though the groundwater is now being recharged in this area, the land subsidence is a permanent feature because the land became so compacted as it sank.
Effects of Groundwater - Natural Features
Natural changes in the landscape from groundwater often come from the interaction of groundwater and limestone. Groundwater comes from rainwater that has soaked into the ground, and the rainwater is naturally acidic because it reacts with carbon dioxide in the air. As it meets with limestone in the ground, it partially dissolves the rock, and as this happens, unique features are formed.
Sinkholes are cavities in the ground caused by erosion of limestone. They are usually funnel-shaped and open to the sky. A sinkhole is formed because the groundwater caves in on itself, but they can also be formed from excessive groundwater removal.
Caves and caverns are underground holes created by the dissolving of limestone. Rainwater moves through the cracks in the limestone and dissolves the rock as it flows through it. Cracks become larger, and this eventually creates large channels underground. It's in this type of landscape that we find true underground rivers. The holes in the rocks are large enough to allow water to flow much faster than if it had to work its way through the soil.
Effects of Surface Water
Surface water benefits the land because it provides energy and transports nutrients and other materials. Because of this, it's also quite efficient at modifying landscapes and creating features on Earth. Water erodes sediments and rocks that are upstream and deposits them downstream. This erosion may be caused by dissolved substances in the water that chemically erode rock material.
The force of the moving water may also cause erosion of sediment and rock materials. Another type of erosion that occurs is when the moving sediments scrape the sides of the stream channels, called abrasion. These sediments and rocks act like sandpaper, carving out holes in the channel and increasing the rate of erosion. When water moves through stream channels, it can create some beautiful features on Earth. Rapids and waterfalls occur in stream channels that are in high mountain areas.
Toward the end of the stream, where the water is moving more slowly, floodplains are created. Floodplains are flat land areas surrounding a stream channel that flood with water and sediments from time to time. When floodplains flood, sediments that were carried with the water are deposited along the stream banks and levees are formed.
Finally, at the very end of the stream (where it meets a large body of water like a lake), the water slows so much that any remaining sediments are deposited, and this forms a delta. Deltas are usually fan-shaped and are areas where land is continually being built as the deposited sediments progressively accumulate.
The constant cycling and movement of water on Earth plays a major role in how Earth's surface is shaped. Many of Earth's landforms are created by moving water, both above and below the land's surface. The speed and composition of the water determines which types of landforms will be created, and landforms created by water may occur naturally or may be influenced by human actions.
After viewing this video lesson, you should be able to:
- Differentiate between groundwater and surface water
- Tell where the saturated and unsaturated zones are found
- Discuss how groundwater can naturally change the landscape
- Understand how humans can change the landscape with groundwater
- Recall the effects of surface water on land