Cordillera Formation, Rock Deformation, and Geological Risks

7. The Formation of Cordillera. The Orogen: Orogens are mountain ranges, their origin linked to subduction zones and plate movements. We can distinguish four types of orogens: island arcs, thermal orogens, collision orogenic, and intraplate orogens.

8. Tectonics. Deformations of the Rocks: Forces produce three types of rock deformation:

• Elastic deformation: A reversible deformation. Rocks deform from sudden shocks but recover their original form. Seismic waves cause this type of deformation.
• Plastic deformation: The folding of rocks, irreversible, usually occurring under intense compression over millions of years.
• Brittle deformation: The rupture of rocks. It happens when they cannot absorb comprehensive or extensional stress with elastic or plastic deformation.

Folds. Geometric Elements:

Folds are plastic deformations of rocks. Four elements classify and help understand their formation:

• Hinge: The part where layers have the greatest curvature.
• Limbs: The sides of the hinge.
• Core: The central part of the fold.
• Axial Plane: An imaginary plane passing through all hinges, with a limb on each side. It's like the fold's symmetry plane.

Types of Folds:

• Anticlines: The oldest layers are enveloped by the youngest. If the axial plane is vertical, limbs point down, and the hinge points up. The core consists of the oldest layers.
• Synclines: The youngest layers envelop the oldest. If the axial plane is vertical, limbs point up, and the hinge points down. The core consists of the youngest layers.

Brittle Deformation. Joints:

Joints and faults are brittle deformations of rocks. Joints are fractures where fragments are not displaced, remaining in their initial position.

Faults. Geometric Elements and Types:

Faults are cracks in rocks with displacement of blocks or lips. The fracture plane is the fault plane.

10. Geological Risks: A situation where a geological process may cause damage to persons or property.

• Risks due to external processes: Floods, torrential floods, droughts, etc.
• Risks due to internal processes: Seismicity, tsunamis, landslides, and volcanic activity.

Measures Against Geological Risks:

• Foresight Measures: Aim to understand the hazard and areas that would be affected. Risk maps are developed.
• Prevention Measures: Designed to prevent the risk or minimize damage if it occurs. Example: Reforestation of slopes with shrubs and trees.
• Prediction Measures: Intended to know as far in advance as possible when and where an event will occur.