Intraplate Phenomena and Plate Tectonics: Earth’s Dynamic Processes
**Intraplate Phenomena**
**Hot Spots**
Hot spots are areas of the land surface that show an exaggerated heat flux due to the rise of solid materials coming from the bottom of the lithosphere. When these materials affect magma, volcanic islands emerge that can remain active for millions of years (e.g., Hawaii).
**Weaknesses**
Weaknesses are fractures in the oceanic lithosphere formed from volcanic materials that emerge through cracks (e.g., Canary Islands).
**Deformation of Rocks**
The movement of plates subjects rocks to different types of stress:
- Compression: Caused by opposing and convergent forces (occurs at ridges).
- Distraction/Tension: A consequence of divergent opposing forces, causing elongation of materials (occurs in subduction zones).
- Shear: Caused by converging and diverging parallel forces, causing displacement.
Depending on the material, deformation can manifest as:
- Folds: Wave-like deformations. These can be classified:
- According to age: Anticline and syncline.
- According to the position in their plane: Straight, bent, stretched, and inverted.
- According to their symmetry: Symmetric and asymmetric.
- Breaks: These can be diaclases or faults.
**Volcanism**
Volcanism refers to the phenomena responsible for the rapid ascent of magma to the surface through eruptions. A volcano is formed by the accumulation of solidified lava and ejecta on the surface. Ejecta can include lava, gases, and solids. Types of volcanoes include shield volcanoes (e.g., Hawaii) and stratovolcanoes (e.g., Pelean).
**Earthquakes**
An earthquake is a sudden movement of the Earth’s crust resulting from the release of energy accumulated over a long period. This can be caused by the formation of a fault or the displacement of blocks along an existing fault.
**Tsunamis**
A tsunami is an earthquake whose epicenter is in the ocean. This causes significant water agitation, resulting in a series of large waves.
**Internal Geological Phenomena in Relation to Plate Tectonics**
**Oceanic Ridges**
An oceanic ridge is a huge mountain range that usually runs through the central regions of the oceans. It has a rift with fractures formed by perpendicular blocks. The central blocks sink, forming a depression that may be occupied by water, thereby forming oceans.
**Formation of Orogenic Belts or Mountain Ranges**
- Island Arc Type: Occurs when there is subduction of oceanic lithosphere beneath oceanic lithosphere (e.g., Japan, Philippines, Marianas).
- Andean or Continental Margin Type: Originates from the subduction of oceanic lithosphere beneath continental lithosphere. The accumulation of sediments over millions of years on a continental margin and the compression between two plates form a deformed tectonic accretionary prism.
- Himalayan or Continental Collision Type: Arises when the oceanic lithosphere of a mixed plate is consumed and subducted beneath a continental margin (e.g., Himalayas, Alps, Urals).
**Plate Boundaries or Edges**
**Constructive Edges**
At constructive edges, plates are separated, and new lithosphere is created (ocean floor). These are associated with oceanic ridges. Phenomena include volcanism, undersea earthquakes, expansion of the oceans, and island formation (e.g., Mid-Atlantic Ridge).
**Destructive Edges**
At destructive edges, one plate subducts beneath another, and the lithosphere is recycled back into the mantle. These are associated with oceanic trenches and uplifted areas on the overriding plate. Phenomena include island arcs, earthquakes, volcanoes, and orogenesis (e.g., the Andes, the Japanese Archipelago, and the Himalayas).
**Passive or Neutral Borders**
At passive borders, lithosphere is neither created nor destroyed. These are associated with transform faults. The main phenomenon is earthquakes (e.g., San Andreas Fault).
**Seafloor**
**Reliefs on the Seafloor**
These include oceanic ridges, seamounts, and deep trenches at continental margins.
**Composition of the Seafloor**
Our understanding of the seafloor’s composition comes from surveys. Volcanic rocks and sediment accumulation are relatively young.