Geological Risks: Understanding Plate Tectonics and Continental Drift

Geological risk is any condition, process, phenomenon, or event that, due to its location, severity, and frequency, can cause health damage or death to humans, economic losses, and environmental damage.

Wilson Cycle

1. First Volcanic Eruptions

Initial magmatism occurs, leaving a long area. It is forming a long fault line that divides the two lithospheric plates.

2. Formation of an Incipient Rift

The fracture of the previous phase is enlarged to be more clearly defined. In the central part of the opening, magma cools, forming oceanic lithosphere. The presence of magma at depth causes lithospheric swelling, forming a thermal dome. A rift valley, surrounded by topographic elevations, lies in the central part.

3. Expansion of the New Ocean Floor

New magma escaping through the opening pushes the previously solidified magma, producing divergent plate movement. Magma output makes the oceanic lithosphere grow and expand the ocean floor until a fracture occurs at a margin contacting the continental lithosphere. A subduction zone begins at this fracture.

4. Subduction

Subduction consumes oceanic lithosphere, approaching the continental lithosphere. Sediments accumulated on the ocean floor are deformed.

5. Closure of the Ocean

The ocean ridge separating the plates may be consumed by the subduction zone. The ocean floor continues to fall as oceanic lithosphere subducts beneath the other, while ocean sediments are compressed until they contact continents.

6. Collision of Continents

When two continents collide, a ridge with many suture lines or deformation bands rises (e.g., the Himalayas). Subsequently, the cordillera erodes until the initial state of the cycle.

Edges Between Types of Plates

Constructive Edges

These areas experience tensile stresses that separate plates. This causes a pressure decrease in depth and the formation of basaltic magma (very fluid). Magma rises between the two plates and solidifies, forging new oceanic lithosphere. Oceanic ridges represent constructive edges.

Destructive Edges

These occur between opposing plates under compression stress. The thinner, denser plate (usually oceanic) dives under the other and melts in the mantle. Oceanic lithosphere is destroyed; this destruction is compensated by lithosphere formation at ridges. Subduction zones are destructive edges.

Neutral Edges

Here, two plates interact via shear stress due to lateral movement. Neither creates nor destroys lithosphere, but friction causes earthquakes, resulting in transform faults.

Risk Factors

Danger

Danger is the probability of a risk occurring with a defined intensity and magnitude. It's established based on the frequency and violence of risk occurrence in a given area. Hazard maps, useful for risk prediction, are developed from this data.

Exposure

Exposure refers to the number of people, animals, or property that may be affected by the risk. Risk is much lower (or zero) in uninhabited areas compared to overcrowded areas.

Vulnerability

Vulnerability quantifies the relationship between casualties or losses and total exposure. Earthquakes of the same magnitude cause very different damage in areas with different economic development levels, even with similar exposure.

Continental Drift Test

Geological Evidence

This is based on the correlation between geological structures (cratons and orogenic belts) on both sides of the Atlantic.

Paleontological Evidence

This is based on the presence of very similar fossil fauna and flora in currently distant continental areas.

Paleoclimatic Evidence

This is based on the location of rocks indicating past weather conditions in regions with currently very different climates.