Seismic Waves, Lithosphere, Tectonic Plates and Volcanoes

Seismic Waves

Seismic waves are the vibrations produced by earthquakes that can travel long distances through the interior of our planet.

Seismographs

Seismographs: instruments where seismic waves are recorded.

Types of seismic waves

P waves

P waves are the most rapid. They spread more rapidly in solid media than in liquid media or in molten material.

S waves

S waves travel more slowly than P waves. They propagate less effectively through liquid media and are often attenuated.

The internal structure of our planet consists of

• Core (core)
• Mantle (composed of dense rock)
• Crust (rocks formed by lighter materials)

Lithosphere

The lithosphere is the outermost layer of the geosphere. It is formed by the Earth's crust and the outermost part of the mantle.

What forms the lithosphere?

Crust and upper mantle.

What is a lithospheric plate?

Gigantic pieces of lithosphere.

Why are plate movements slow?

The plates float on partially molten rock and move slowly as a result of mantle convection and other geodynamic processes.

Types of boundaries between tectonic plates

• Convergent (tapering) boundaries: where two tectonic plates converge.
• Divergent boundaries: where tectonic plates separate.
• Transform (strike-slip) boundaries: where tectonic plates slide laterally past one another.

Types of lithosphere

Continental lithosphere

The continental lithosphere extends beneath continents and is formed by rocks of lower density.

Oceanic lithosphere

The oceanic lithosphere is located beneath the ocean floors. It is a thinner layer formed by rocks denser than those of the continental lithosphere.

Volcanoes

Volcanoes are openings or cracks through which molten material from within the geosphere is expelled.

Volcano structure

• Magma chamber: the location of the magma.
• Volcanic pipe: the conduit through which magma rises.
• Crater: the outlet of the molten material.
• Lava flows: molten material that flows down the slopes of the volcano.
• Volcanic cone: the volcanic mountain formed by the accumulation of lava and other products expelled by the volcano.

Types of Volcanoes

• Subaerial volcanoes: those that erupt on land (inland areas).
• Submarine volcanoes: volcanoes whose activity takes place below the sea surface.

Volcanic Hazards

Volcanic activity can cause catastrophic effects from the emission of lava, pyroclastic (burning) clouds, poisonous gases, and ash fall.