Earth's Dynamic Geology: Processes, Relief, and Risks

Magmatism and Volcanism

Magmatism and volcanism are fundamental geological processes related to the formation of magma and volcanoes.

Magmatism: Formation of Magma and Rocks

Magmatism is the process involving the formation of magma (a mixture of melted materials with minerals and gases) and magmatic rocks (formed from the consolidation of magma). Conditions conducive to rock fusion include:

• Temperature increase: Elevated temperatures cause rocks to melt.
• Pressure decrease: Reduced pressure allows rocks to expand and, consequently, melt.
• Presence of fluids: Water, in particular, significantly lowers the melting point of rocks.

Volcanism: Magma Reaching the Surface

Volcanism is the process by which magma reaches the Earth's surface, forming volcanoes and other materials such as volcanic rocks. There is a strong relationship between volcanism and plate tectonics. More than 80% of volcanoes are found in mid-ocean ridges and subduction zones:

• Mid-ocean ridges: Rocks melt and magma forms under conditions of:
  • Lower lithospheric pressure.
  • Very thin lithosphere.
• Subduction zones: Rocks melt and magma forms due to:
  • Strong friction between the two converging plates.
  • Water lowering the melting point of rocks.
• Lithospheric plate interiors: Rocks melt and magma forms in these areas, typically occurring at hotspots.

Metamorphism and Seismicity

Metamorphism encompasses the formation of metamorphic rocks. This process is closely related to seismicity, a phenomenon that includes the appearance of earthquakes.

Metamorphism: Rock Transformations

Metamorphism refers to the transformations that rocks undergo to form metamorphic rocks. These changes are influenced by various factors:

• Temperature: An increase in temperature produces changes in the crystals of minerals.
• Pressure: High pressure alters mineral crystals and prevents magma from forming.
• Fluids with chemicals: These fluids aid in the formation of new minerals.

The most common areas with metamorphism are:

• Subduction zones: Characterized by very high pressure and temperature.
• Continental collision zones: Exhibit similar conditions to subduction zones.

Seismicity: Understanding Earthquakes

Earthquakes are caused by movements between lithospheric plates. The release of accumulated energy in the rocks is transmitted as seismic waves. Most earthquakes originate at plate boundaries:

• Subduction zones: These zones experience earthquakes of great magnitude, occurring in three depth areas:
  • Shallow earthquakes: Up to 70 km deep.
  • Intermediate earthquakes: Between 70 and 300 km deep.
  • Deep earthquakes: Between 300 and 660 km deep.
• Oceanic ridges: Typically experience earthquakes of lesser magnitude.
• Transform faults: Known for earthquakes of high magnitude.

Earthquakes have different parts.

Geological Processes and Earth's Relief

Geological processes fundamentally determine the relief on Earth.

Earth's Relief: Surface Formations

Relief is the set of geographic formations that occur on the Earth's surface due to the interplay of internal and external geological processes. There are mutual influences:

• Internal processes influence external processes.
• External processes influence internal processes.

Types of Geological Processes

Geological processes can be categorized as internal or external:

• Internal geological processes: Powered by Earth's internal heat and gravity.
  • Main agents: Movement of lithospheric plates and gravity.
  • Events: Earthquakes and volcanoes, which build and uplift the relief.
• External geological processes: Powered by solar energy and gravity.
  • External agents: Water, ice, wind, atmosphere, and living organisms.
  • Events: Weathering, erosion, transport, and sedimentation, which destroy and shape the relief.

Topographic Maps: Representing Relief

Topographic maps are forms of representing the relief, featuring various elements:

• Contour lines: Lines connecting points of equal elevation.
• Scale: The relationship between map distance and real-world distance.
• Equidistance: The elevation difference between two consecutive contour lines.

Understanding Geological Risks

Geological risks are threats originating from natural geological processes. These risks can cause damage to human beings, their belongings, and infrastructure.

Risk is often defined by the equation: Risk = Danger + Vulnerability

• Danger: The probability of a phenomenon occurring in a specific place at a certain time.
• Vulnerability: The value of potential damages that people or their belongings can suffer as a consequence of the phenomenon.

Seismic Risk: Earthquakes and Their Impact

Seismic risk is specifically associated with earthquakes. The incidence is almost one million per year. The measures of earthquakes are:

• Magnitude: The energy released at the hypocentre, typically expressed by the Richter scale.
• Intensity: The damage caused in a certain area.

The main effects of earthquakes are:

• Landslides: Movements of mud and rocks.
• Fires: Often caused by the destruction of underground gas and water pipelines.
• Tsunamis: Caused by large earthquakes that affect the ocean floor.

In Spain, seismic risk is primarily located in the Mediterranean region.