Earthquakes and Volcanoes: Types, Distribution, and Eruptions

Posted on Jan 31, 2025 in Geology

Earthquakes According to Their Origin

There are two main types of earthquakes: tectonic and volcanic.

Tectonic Earthquakes

These are produced by the movement of rock masses along faults or tears and friction between plates. These earthquakes may occur due to different processes and are distinguished by depth:

  1. Those that happen because of the movement of two blocks along a fault. Their hypocenter is located at shallow depths, generally less than 50 km. They are the most intense and, therefore, the most catastrophic.
  2. Those that occur in subduction zones where an oceanic plate is inserted into the mantle. The hypocenters may be at different depths along the subduction plane and are registered up to 700 km deep.

Volcanic Earthquakes

These are caused by underground magma movement and eruptions that are sometimes violent.

Distribution of Earthquakes in Relation to Plate Boundaries

Earthquakes are distributed in three large regions:

  1. A belt of high seismicity around the Pacific. This corresponds to the zone where the Pacific plate is subducted, as well as the Nazca and Cocos plates.
  2. The second belt of intense seismic activity stretches from the Azores to Gibraltar, across the Mediterranean Sea to Indonesia.
  3. The third high seismic belt runs through the center of the Atlantic Ocean, where it divides into two branches, one for the Indian Ocean and the other for the southern Pacific Ocean. This corresponds to the areas of mid-ocean ridges.

Volcanoes

Most volcanoes are located in active areas on the planet: young mountain ranges, mid-ocean ridges, transform faults, and subduction zones.

Note also the existence of volcanoes in the interior of a plate in so-called hot spots where magma rises from the deep mantle. Volcanoes are arranged in the following areas:

  1. Constructive boundaries in mid-ocean ridges, like the numerous volcanoes of Iceland and Cape Verde.
  2. Destructive boundaries in subduction zones, like Cotopaxi in the Andes and Krakatoa in Indonesia.
  3. Neutral boundaries where shear occurs (like Vulcano and Etna).
  4. Hot spots like the islands of Hawaii, located on the Pacific plate. On Hawaii’s largest island of the archipelago, there are three active volcanoes: Mauna Loa, Kilauea, and Hualalai.

Volcano Structure

Volcanoes are geological structures through which magmas originating in the interior of the Earth, in the lower crust or the mantle, rise to the surface. When the volcanic material is ejected by large fractures, it forms fissural volcanoes; if done by a single point, a volcanic cone or central volcano forms.

  1. In fissural volcanoes, the magma rises through fractures, which can be up to 25 km in length and 15 m in width.
  2. In central volcanoes, magma accumulated in the magma chamber rises through fractures, the chimney, and out of the crater.

Volcanic Eruptions

Terrestrial Volcanic Eruptions

  • If the magma is fluid, the gases are released slowly and easily and produce almost no explosive activity.
  • If the magma is viscous, the egress of gases is difficult. These gases accumulate and exert enormous pressure. When abruptly released, there are strong explosions.

Submarine Volcanic Eruptions

  • When eruptions are superficial, they are usually very violent because the lava occurs as underwater explosions in contact with seawater.
  • If eruptions occur more than 300 m deep, the lava emerging quickly solidifies on contact with water to form lava pillows or pillow lavas.