Endogenic Processes and Earthquakes

Endogenic Processes

• An internal geomorphic process driven by Earth's internal energy
• Includes tectonic movements, metamorphism, seismic activities, and magmatism
• Primordial heat is leftover heat from Earth's formation
• Radioactive heat comes from the decay of radioactive elements
• Volcanism is the eruption of molten rock (magma) onto the surface
• Magma's viscosity (resistance to flow) depends on temperature, silica content, and dissolved water. Higher silica and lower temperature increases viscosity making magma less fluid.
• Mafic magma (low silica) is less viscous than silicic (high silica) magma
• Earthquakes are ground shaking caused by sudden movement of rock beneath the Earth's surface.

Earthquakes

• A weak to violent shaking of the ground produced by sudden movement of rock materials below the surface
• The surface where the rocks slip is called the fault plane
• Focus is the location at depth where the slip occurs
• Epicenter is the location on the surface directly above the focus

Exogenic Processes

• Occur on or near the Earth's surface, typically driven by gravity, water, wind, and organisms
• Weathering is the breakdown of rocks into smaller pieces or into different substances
• Physical weathering breaks rocks into pieces without changing their composition.
• Factors are: pressure, temperature changes, frost wedging, and abrasion.
• Chemical weathering involves reactions between rocks and chemicals causing changes in minerals
• Dissolution is the dissolving of rocks by acidic waters
• Hydrolysis is when minerals react with water to form new solutions
• Oxidation is when oxygen reacts with minerals, a classic example being rust.

Release of Pressure (Exfoliation)

• Pressure release can cause outside layers of a rock to crack and flake off
• Repeated expansion and contraction of water freezing in cracks causes cracks to widen and eventually the rock to break apart

Types of Stress

• Differential stress - involves forces pulling or pushing in different directions
  • Tensional stress: stretching and thinning of rocks, associated with divergent plate boundaries
  • Compressional stress: pushing rocks together, thickening and folding, associated with convergent plate boundaries
  • Shear stress: forces acting parallel but in opposite directions, causing blocks of rock to slide past each other, associated with transform plate boundaries
• Uniform stress - involves equal forces in all directions

Deformation of Earth's Crust

• Deformation is the process of changing the shape or volume of the crust, often caused by stress along tectonic plate margins.
• This creates important geological features. 
• Geological features include folds, faults, foliations and joints.
•  Folds are bends or curves in rock layers
•  Faults are fractures in rock layers where movement has occurred
•  Foliations are planar structures in metamorphic rocks.
•  Joints are fractures in rock layers.

Stages of Deformation

• In elastic deformation, deformation is reversible.
• In ductile deformation, deformation is permanent.
• In brittle deformation (fracturing), deformation results in breakage.

Products of Deformation

• Faults: fractures in rock where movement has occurred
• Folds: bends or curves in rock layers

Types of Folding

• Anticlines are upward-arched folds.
• Synclines are downward-arched folds.
• Monoclines are step-like folds.

Types of Faults

• Normal faults: hanging wall moves down relative to the footwall (tensional stress)
• Reverse faults: hanging wall moves up relative to the footwall (compressional stress)

Seafloor Spreading

• A geologic process where new oceanic crust is formed at mid-ocean ridges
• Older rocks move away from the ridge
• Proposed by Harry Hess; supported by sonar mapping of the mid-Atlantic Ridge and other evidence.