Plate Tectonics, Volcanoes, and Seismic Activity

Do the Continents Move?

Types of Lithospheric Plates

• Oceanic plates are composed of oceanic lithosphere.
• Continental plates are composed of continental lithosphere.
• Mixed plates consist of both continental and oceanic lithosphere.

The Mechanism of Plate Movement

The movement of lithospheric plates occurs because materials in the deepest part of the terrestrial mantle, found at high temperatures, rise from the interior of our planet until they cool enough to descend again. This creates high-movement cycles of mantle material called convection currents.

Major Lithospheric Plates

• Juan de Fuca Plate
• North American Plate
• Pacific Plate
• Cocos Plate
• Caribbean Plate
• Nazca Plate
• South American Plate
• Scotia Plate
• Antarctic Plate
• African Plate
• Arabian Plate
• Eurasian Plate
• Indo-Australian Plate

Plate Interactions and Drift

When the plates move away from each other, there is a rise of materials from the planet's interior, causing volcanic eruptions and the formation of large submarine elevations called oceanic ridges.

When two plates collide and one slides under another, the process is known as subduction. This originates volcanoes, strong earthquakes, and the formation of mountain ranges.

When plates slide relative to one another, it causes great earthquakes.

Volcanic Products and Classifications

Liquid, Gaseous, and Solid Products

• Liquid products: Molten lava at temperatures superior to 1,000 degrees Celsius.
• Gaseous products: These emerge from the magma and consist mainly of water vapor, hydrogen sulfide, and carbon dioxide.
• Solid products (pyroclastics): These are classified by size:
  • Ash: Particles less than 2 mm in diameter.
  • Lapilli: Pebbles with a diameter between 2 and 64 mm.
  • Volcanic bombs: Rounded volcanic rocks over 64 mm.

Types of Volcanoes

Hawaiian Volcano: Fluid magma accumulates as gas escapes easily, producing tranquil eruptions and extensive lava flows, such as the Kilauea volcano on the island of Hawaii.

Strombolian Volcano: The magma is less fluid than in Hawaiian volcanoes, so abundant landslides occur with moderate gas explosions and extensive lava flows.

Peléan Volcano: This features very viscous magma where gases escape with difficulty, originating highly explosive eruptions.

Understanding Earthquakes

Earthquakes are sudden movements of the upper layers of the Earth produced by the fracture and subsequent displacement of large rock masses inside the crust.

Elements of an Earthquake

• Hypocenter: The place of origin of the earthquake and the source of seismic waves.
• Epicenter: The point on the Earth's surface vertically above the hypocenter where waves reach the surface and the effects of the quake are perceived with the most intensity.
• Seismic waves: Vibrations from the earthquake hypocenter that transmit movement in all directions through space and can produce catastrophes.

Volcanic Risks and Hazards

• The issuance of lava
• Gas emissions
• Rain of pyroclastics
• Burning clouds (pyroclastic flows)
• Melting ice