Volcanic Structures, Activity Types, and Landforms

Posted on Jan 23, 2025 in Geology

Volcanic Relief

Structure of a Volcano

  • Crater: Orifice where volcanic products exit the surface.
  • Volcanic Cone: Structure formed by the accumulation of volcanic material around the crater.
  • Chimney: Tube that connects the magma chamber to the crater, where the magma exits.
  • Magma Chamber: Deposit in which magma accumulates before going outside.

Volcano Types

Depending on the characteristics of the material ejected, volcanoes have different types of structures:

  1. Pyroclastic Cone: Small, with very steep walls, caused by the accumulation of pyroclasts, consisting of loose material, and has little height.
  2. Shield Volcano: Very broad-based cone formed by eruptions of very fluid lava that solidifies far from the crater.
  3. Stratovolcano: Pyroclastic cone formed by lava that gives great height; Teide and Vesuvius are of this type.
  4. Volcanic Dome: Dome-shaped, caused by the release of highly viscous lava that solidifies around the crater.

Calderas

A caldera is a large, circular depression larger than a crater, with a dimension of several kilometers. Three types are distinguished:

  1. Explosion Caldera: Caused by the explosion of a volcano.
  2. Erosion Caldera: Caused by the removal of surface materials.
  3. Collapse Caldera: Caused by the collapse of building materials into a shallow, half-empty magma chamber.

Other Volcanic Landforms

Volcanic formations are formed by:

  1. Dikes: Originate to fill fractures, and magma solidifies inside.
  2. Sills: Tubular bodies, parallel to bedding or exchanged between layers of pyroclasts.
  3. Volcanic Necks: Circular dams caused by the solidification of magma in the outlet conduit.

Types of Volcanic Activity

There are two types of volcanic activity: explosive and effusive.

Volcanic activity depends on:

  1. Gas Content: The accumulation of gases in the magma chamber or in the outflow increases volcanic activity.
  2. Shape and Features of the Volcanic Edifice: When the volcano has a deep, narrow chimney that is packed, the gases accumulate and cause explosions.
  3. Viscosity of the Lava: Viscosity indicates a liquid’s resistance to flow; if it flows easily, it is very fluid; on the contrary, it will be viscous.

Viscosity is characterized by:

  1. The composition of the lava, rich in silica.
  2. Temperature: The lower the temperature, the more viscous the lava.
  3. Content of solid materials: The presence of crystals gives more viscosity.

Effusive Activity

Shown in its crater as a lake of lava.

Gases escape easily. The magma chamber is filled and overflows the crater, and fast lava flows arise.

For example, Kilauea (Hawaii).

The lava is basaltic with low viscosity.

Gases do not accumulate; lava gradually reduces the number of explosions.

They form few pyroclasts; lava is at a low temperature, and there are few explosions.

Explosive Activity

On May 18, 1980, in the United States, the most violent eruption of the last 1000 years occurred. The St. Helens volcano erupted, throwing gas and pyroclasts that razed forests, causing around 59 deaths. This volcano is an example of explosive activity and is characterized by:

  • The lava is very viscous; it solidifies and clogs up the outlets.
  • Gases accumulate, and the pressure causes explosions.
  • Pyroclasts originate and can cause low clouds at ground level that move at high speed and sweep everything in their path; these are called burning clouds.

Within volcanic activity, we find different levels of explosiveness, called:

Strombolian, Vulcanian, and Plinian, the most violent.