Mountain Formation and Tectonic Plate Interactions

The Formation of Mountains

The thickening of the crust, caused by the collision of continents, results in mountain ranges. The relief is formed by the collision of lithospheric plates, by volcanic activity, or hot spots in the crust. Both mechanisms are related to upstream and downstream flows that exist in the mantle.

• Oceanic Ridges: Present intense volcanic activity.
• Oceanic Trenches: Deep areas of the oceans.
• Abyssal Plains: Flat underwater areas, are the most extensive.
• Submarine Volcanoes: Isolated reliefs, which in some cases emerge from the ocean and cause volcanic archipelagos.

Interaction of Internal and External Processes

Isostatic movements are vertical movements of the lithosphere, which tends to sink in some places and rise in others.

Folds and Faults

Faults

A fault is a fracture of the land, in which fragments or resulting blocks are displaced.

Parts of a Fault

• Fault Plane: The plane along which the fracture occurs and the displacement of the ground.
• Dip: The angle of the fault plane with the horizontal.
• Strike: The angle of the fault plane with respect to the northern region.
• Fault Scarps: Each block of land at two sides of the fault plane is called a scarp, either uplifted or sunken.
• Fault Throw: Displacement between the two scarps of the fault.

Types of Faults

• Normal: Arises from divergent forces on the ground that fracture and, as a result, sink a block. Appears in rift zones.
• Reverse: Created by converging forces on the ground that fracture, and consequently, raise a block. Appears in collisions between lithospheric plates.
• Transform: Lateral forces moving blocks of land, without sinking or lifting.

Folds

A fold is a ripple in the layers of rocks produced by compressive forces.

Parts of a Fold

• Hinge: Area of maximum curvature.
• Limbs: Each side of a fold.
• Axial Plane: A plane that unites all hinge lines of folded strata.
• Plunge: Angle with the horizontal axial plane.
• Dip: The angle that a limb forms with the horizontal.
• Strike: The angle that the axial plane forms with the northern region.

Types of Folds

• Anticline: The layers are convex and the hinge is the most elevated part of the fold.
• Syncline: The strata are concave, the hinge is the lower part of the fold.
• Upright: A fold with a vertical axial plane, now verging on 90 degrees.
• Inclined: A fold with a vergence of less than 90 degrees.
• Recumbent: Fold with a highly inclined or nearly horizontal axial plane.