Horst and Graben

Download PDF

What is Horst and Graben?

Bookmark added to your notes.
View Notes

Horst Meaning- A horst is a raised fault block bounded by natural faults in physical geography and geology. A horst is a raised block of the Earth's crust that has lifted or stayed stationary while the land around it (graben) has sunk.

Horst and Graben are found together in an extensional environment. The graben is the block that has been downthrown, while the horst is the block that has been upthrown next to the graben.

What is the Meaning of Horst?

Horst meaning: Horst is a Dutch and German word that means heap and is similar to the English word "Hurst."

What is the Meaning of Graben?

A graben is a fault block that has been lowered relative to the blocks on each side without significant interference or tilting. Bordering faults, or fault zones, are usually of near-parallel strike and steeply dipping, with nearly equal vertical displacement. The relative movement of the blocks that define a graben Both of the blocks may have rotated according to their initial positions, but the middle block may have subsided further than the outer two. As a result, a true graben in its original surface shape is a linear structural depression. The scale of grabens varies widely, but the superiority of a long fault trough is a distinguishing feature.

Geomorphology of Horst

The cross-sections of horsts may be symmetrical or asymmetrical. The horst is likely to be symmetrical and approximately flat on top of the usual faults on either side have identical geometry and are moving at the same rate. The top of the horst would most likely be inclined and the entire profile would be asymmetrical if the faults on each side have different rates of vertical motion. In cross-section, erosion has a big influence on how symmetrical a horst looks.

[Image will be Uploaded Soon]

Horst and Graben Formation

Horst and graben are formed when opposite-dip natural faults with parallel strike lines occur in pairs. They are inextricably linked. Horsts and grabens may be as small as a few centimetres wide or as large as tens of kilometres wide, with vertical movement of several thousand feet. They're bordered on both sides by steeply dipping regular faults, which have virtually equivalent movement, resulting in blocks that are barely tilted. The faults that form horsts tend to dip away from each other, while those that form grabens tend to dip against each other. Two or more horsts and grabens can be found close together.

They're thought to be caused by lateral stress, which could be caused by regional uplift or salt dome formation; they're most common on dome crests or anticlines.

Hydrocarbon Exploration and Horsts

The vast majority of discovered hydrocarbons in many rift basins around the world are located in traditional traps associated with horsts.  Most of the petroleum discovered in Libya's Sirte Basin (tens of billions of barrels of reserves) is located on large horst blocks like the Zelten Platform and the Dahra Platform, as well as smaller horsts like the Giallo High and the Bu-Attifel Ridge.

Examples of Horst and Graben Formation

Wallonia's Condroz and Ardennes regions are strong examples of horst and graben succession.

The Satpura Range is a horst in India, flanked to the north by the Narmada Graben and to the south by the much smaller but parallel Tapi Graben.

The Vosges Mountains in France and the Black Forest in Germany are examples of horsts, as are the Table, Jura, Dole Mountains, and the Rila - Rhodope Massif, which includes the well-defined horsts of Belasitsa (linear horst), Rila mountain (vaulted domed shaped horst), and Pirin mountain (a horst forming a large anticline situated between the complex graben valleys of Struma and that of Mesta.

FAQ (Frequently Asked Questions)

Q1. Is Graben a Rift Valley?

Ans) Rift valleys are valleys formed in grabens that may exhibit vulcanism, which is often associated with graben formation. The Jordan–Dead Sea depression and Death Valley are examples of grabens. The French Vosges Mountains and the Palestine Plateau are also examples of horsts.

Q2. What Kind of Stress Produces a Graben?

Ans) Graben are formed by parallel normal faults with the hanging wall displacing downward and the footwall displacing upward. From both sides, the faults usually dip toward the graben's base.

Q3. Where does the Term ‘Horst’ Come From?

Ans) The word means "man from the forest," "bosk," or "brushwood" in Old High German. "Horst" is also the modern German version of the English aerie or eagle's nest.

Q4. What is a Horst Mountain?

Ans) A block mountain, also known as the horst, is formed when a piece of land is uplifted between two faults. As a result, a horst is a piece of land that has been raised, resulting in the creation of a peak.