Bedrock is the hard, solid rock beneath surface materials such as soil and gravel. Bedrock also underlies sand and other sediments on the ocean floor. Bedrock is consolidated rock, meaning it is solid and tightly bound. Overlying material is often unconsolidated rock, which is made up of loose particles.
Bedrock can extend hundreds of meters below the surface of the Earth, toward the base of Earth's crust. The upper boundary of bedrock is called its rockhead.
Above the rockhead, bedrock may be overlain with saprolite. Saprolite is bedrock that has undergone intense weathering, or wearing away. Saprolite has actually undergone the process of chemical weathering. This means saprolite is not just less-consolidated bedrock, it has a different chemical composition. Flowing water or ice has interacted with minerals in the bedrock to change its chemical make-up.
Above the saprolite may be layers of soil, sand, or sediment. These are usually ofter, younger, and unconsolidated rocks.
Exposed bedrock can be seen on some mountaintops, along rocky coastlines, in stone quarries, and on plateaus. Often, these visible exposures of bedrock are called outcroppings or outcrops. Outcrops can be exposed through natural processes such as erosion or tectonic uplift. Outcrops can also be reached through deliberate drilling.
People and Bedrock
Identifying bedrock is an important part of geology, stratigraphy, and civil engineering.
Science
Geology is the study of rocks and minerals. Stratigraphy is the study of rock layers (stratification). Stratigraphers study the way rocks, and their relationships to each other, change over time.
Determining the depth and type of bedrock helps geologists and stratigraphers describe the natural history of a region.
For instance, the southern part of the U.S. state of Indiana has exposed bedrock. The northern part of the state is covered by meters of soil and unconsolidated rock. This landscape offers geologists a clue about how far glaciers extended during the Ice Age. The thick soil of northern Indiana was in part created as giant glaciers carved across the region's rockhead, grinding it into unconsolidated gravel. The bedrock of the southern part of the state experienced less weathering and erosion, and was left with less glacial till as the glaciers retreated.