Earth’s Internal Heat: Volcanoes, Earthquakes, and Plate Tectonics

Posted on Feb 25, 2025 in Geology

Earth’s Internal Heat

The Earth’s internal heat was formed by:

  • Meteorite impacts
  • The collapse of iron, which generates heat by friction
  • Radioactive decay of elements like Uranium and Plutonium, emitting energy as radiation

Manifestations of Internal Heat

The Earth’s internal heat manifests in several ways:

  • Volcanism: Magma rises to the surface from deep within the crust.
  • Earthquakes: Sudden, jerky movements of the Earth’s crust.
  • Continental Drift: Horizontal displacement of continents.
  • Isostasy: Slow vertical movements of the Earth’s crust, causing some areas to sink and others to rise.

Volcanism

Magma is a mixture of molten rock and gases, primarily formed in the inner mantle. It tends to rise towards the surface. If it finds an outlet through a fracture, it produces a volcanic eruption.

Volcanic Products

Volcanoes eject materials in three states:

  • Liquids: Lava
  • Solids (Pyroclastics):
    • Rock fragments thrown into the air
    • Volcanic bombs
    • Lapilli (gravel-sized fragments)
    • Volcanic ash (sand-sized fragments)

Types of Volcanic Activity

There are three main types of volcanic activity:

  • Hawaiian: Highly fluid lava flows with few pyroclastics.
  • Strombolian: Viscous lava flows with abundant pyroclastics.
  • Vulcanian: Gases and ash mixed with abundant pyroclastics.

Earthquakes

Earthquakes are caused by vibrations resulting from sudden movements of the Earth’s crust. These vibrations are transmitted as waves through the Earth’s interior. The point where the failure occurs is called the hypocenter. The area on the Earth’s surface directly above the hypocenter is the epicenter.

Vibrations are transmitted inside the Earth as seismic waves. The magnitude of an earthquake is measured using the Richter scale.

Earth’s Structure

The Earth’s structure is divided into layers: the core, the mantle, and the crust. Between the crust and mantle are lithospheric plates, of which there are three types:

  • Lithospheric plates
  • Oceanic plates
  • Mixed plates

Movements of the Lithosphere

The lithosphere is broken into huge fragments. The Earth’s internal heat causes convection currents in the mantle beneath the lithosphere. These currents push the lithospheric plates, causing them to move in three ways:

  • Separating: Two plates move away from each other, allowing material from the mantle to surface, producing volcanism. The rift between the two plates is called a rift zone.
  • Colliding: Two plates collide, creating a subduction zone.
  • Sliding: Two plates slide past each other, giving rise to earthquakes.

Volcanoes, Earthquakes, and Plate Tectonics

Plate tectonics explains the causes and consequences of lithospheric plate motions. The consequences include:

  • Seismicity (earthquakes)
  • Volcanism
  • Subduction of the lithosphere
  • Formation of new oceanic lithosphere in rift zones
  • Folding and fracturing of rock
  • Formation of relief (landforms)

Formation of Mountains

Mountains form when magma rises, cools, and causes continents to move and collide. The collision of continents leads to the formation of mountain chains. There are two types of relief formed by:

  • Collision of continents
  • Volcanic activity in hot areas of the crust

Interaction of Internal and External Processes

Isostatic movements are vertical displacements of the lithosphere, causing some areas to sink and others to rise. There are two types of isostatic movements:

  • Subsidence: Sinking of the lithosphere.
  • Isostatic Rise: Uplift of the lithosphere.