A horst is a geological feature representing an uplifted block of the Earth's crust that lies between two parallel normal faults.
Understanding a Horst
A horst is characterized by its distinct elevation and formation process. It stands out as a raised landform compared to the surrounding areas.
Key characteristics of a horst include:
- Location: A horst is situated specifically between two normal faults. Normal faults are a type of fault where the hanging wall moves down relative to the footwall, typically occurring in areas where the crust is being pulled apart.
- Elevation: The block of land forming the horst is higher than the regions located beyond the bounding faults. This elevated position gives horsts their characteristic appearance as ridges or elevated plateaus.
- Formation: Horsts are formed as a direct result of the extension of the Earth's crust. When the crust is stretched or pulled apart, tensional forces cause sections of the rock to break and move, leading to the development of normal faults. The central block caught between these downward-moving fault blocks is then uplifted relative to its surroundings.
How a Horst is Formed
The formation of a horst is intrinsically linked to the dynamics of tensional stress within the Earth's crust.
- Crustal Extension: The process begins when the Earth's crust experiences tensional forces, meaning it is being stretched or pulled apart. This often occurs in areas of divergent plate boundaries or regional extension.
- Faulting: As the crust stretches, it eventually fractures, leading to the formation of normal faults. These faults are typically dip-slip faults where the rocks above the fault plane (hanging wall) move downward relative to the rocks below (footwall).
- Block Uplift: When two normal faults dip away from each other, the block of land caught between them can be uplifted, or remain relatively stable while the adjacent blocks on the outer sides of the faults drop down. This creates the elevated landform known as a horst. Conversely, a downdropped block between two normal faults is known as a graben.
The interplay of these tensional forces and the resulting faulting creates the distinctive alternating landscape of elevated horsts and subsided grabens, a common feature in rift valleys around the world.
