Volcanoes, Earthquakes, and Plate Tectonics: Earth’s Dynamics

Posted on Dec 14, 2024 in Geology

Volcanoes

A volcano is any crack in the Earth’s surface through which incandescent material emerges from within.

Some well-known volcanoes are:

  • Teide, Spain
  • Vesuvius, Italy
  • Parinacota, Chile

Some volcanoes are conical mountains, while others are in the deep sea and are shaped like cracks.

Why Do Rocks Melt?

At about 100 km depth, the temperature is 1300°C. Despite the high temperatures inside the Earth’s crust and mantle, rocks are in a solid state. The rocks melt due to:

  • Temperature: In this area, it is higher than average.
  • Pressure: It decreases, causing the rock to melt.
  • Water: Its presence facilitates the fusion of rock.

How an Eruption Occurs

Along with the liquid fraction, magma contains solid materials that have not yet been merged or solidified. Magma originates in deep areas. On its way to the surface, magma collects in a magma chamber. When the chamber is filled, it erupts because of:

  • Increased pressure: The magma chamber walls expand and break.
  • Gas escape: Gases escape and drag the rest of the magma.

Volcanic Products

The materials ejected from volcanoes are:

  • Gases: These are the first materials to go outside, formed by water vapor from groundwater and ice. They can also include CO2, sulfur dioxide, etc.
  • Lavas: Molten material that comes out of the mouth of the volcano, forming streams called lava flows.
  • Pyroclasts: Solid materials that go abroad with gases. They are classified according to shape and size as:
    • Ash: Smaller than 2 mm.
    • Lapilli: Pyroclasts between 2 and 64 mm.
    • Blocks: Larger than 64 mm with irregular shapes. If they are round, they are called bombs.

Continents Adrift

There are seven major lithospheric plates, and between them are about a dozen smaller plates. The movements of lithospheric plates produce earthquakes. The continents are part of these plates and travel with them. It has been shown that the European continent is separated by 2 cm each year from Africa, and North America is distanced from South America by 3 cm per year.

Moving Lithospheric Plates

An erupting volcano shows us that the Earth’s interior is at a high temperature, between 1000 and 3500°C. Due to the pressure exerted by the materials above them, the rocks are solid but ductile. Mantle materials are subject to cyclical movements called convection currents.

Earthquakes

An earthquake, also called a seism or a tremor, is a ground vibration produced by a sudden release of energy. It occurs when large masses of rock break. These cracks are called faults.

The place where the earthquake originates is called the seismic focus or hypocenter. From the hypocenter, seismic waves are transmitted in all directions.

The seismic source is located inside the Earth at a depth of about 700 km. The point on the land surface closest to the hypocenter is called the epicenter. A seism can last between 20 and 60 seconds, although there are shocks that can last for several minutes. After the main earthquake, smaller aftershocks may follow.

The devices that record and measure earthquakes are called seismographs, which draw graphs called seismograms.

Magnitude and Intensity of Earthquakes

  • Magnitude of an earthquake: The amount of energy released, measured by the Richter scale, in which each level corresponds to 33 times the energy of the previous level.
  • Intensity of an earthquake: The measure of impact on people, buildings, and terrain.

Intensity was once measured with the Mercalli scale, and an updated modern version is the MSK scale.

Each earthquake has one magnitude, while its intensity decreases as we move away from the epicenter.

Tsunamis

The term tsunami is of Japanese origin, meaning “harbor wave”. Tsunamis are huge waves caused by a sharp rise in a large mass of water at the bottom of the sea. Most tsunamis are caused by earthquakes whose epicenter is under the sea, volcanic eruptions, landslides, or impacts of meteorites.

Minutes before the arrival of the big wave, there is a withdrawal of the sea, trapping many people. A tsunami may reach 30 m in height, although the destruction is due to its great length and the volume of water it displaces, which can penetrate several kilometers inland.

Plate Tectonics

The theory of plate tectonics explains why the continents drift and why volcanoes and earthquakes are located in certain areas. The basic ideas are:

  • The lithosphere is divided into lithospheric plates.
  • The inside of the Earth is at high temperatures, which makes the material subject to convection currents.
  • Convection currents in the mantle move the lithospheric plates.
  • Plate motions cause the separation and union of continents and cause large ranges such as the Himalayas, the Andes, and the Pyrenees.