VOLCANIC ERUPTIONS

Volcanic Eruptions

• Eruptions of volcanoes are among the most formidable and disastrous phenomena on our planet.
• They emerge from the intricate interaction of geological processes occurring below the Earth's surface, mostly influenced by the motion and characteristics of magma. 
• Magma is a liquefied rock located deeper in the Earth's crust.
• A major contributor to the development of igneous rocks, it plays a crucial role in volcanic activity.
• Upon reaching the Earth's surface and erupting, magma undergoes a transformation into lava, which, upon solidification, becomes an essential component of the Earth's crust.

Geological origins of magma

Comprehending the origins of magma is essential for the analysis of volcanic activity. Presented below are the main sources:

1. Phased melting of mantle rocks

Geographical distribution: This phenomenon is predominantly seen in the upper mantle.

Mechanism: Elevated temperature and pressure can cause the liquefaction of mantle components, resulting in the formation of magma.

Chemistry: This lava is usually basaltic, distinguished by its low silica concentration.

2. Crystallographic Melting

Geographical Distribution: This often takes place in continental crust environments.

Mechanism: Convection from underlying magma can cause the melting of the overlying crust, resulting in the creation of magma with different compositions.

Composition: Typically leads to the formation of silicic (felsic) magmas, such as andesite and rhyolite.

3. Zones of Subduction

• Process: Subduction of an oceanic plate beneath a continental plate results in the release of water by the descending slab, therefore reducing the melting point of local rocks.
• Outcome: This process produces magma with intermediate to silicic composition, which is often accountable for triggering violent volcanic eruptions.

4. Hotspots

• Regions where magma originating from the Earth's mantle undergoes melting above the Earth's crust.
• The Hawaiian Islands, born from a volcanic hotspot, predominantly produce basaltic lava.

Classification of Magma

Distinct characteristics of various kinds of magma impact the manner of eruptions and the volcanic landscape.

1. Magma of basaltic origin

• Characteristics: minimal viscosity, modest silica concentration.
• Eruption Style: Typically non-explosive, resulting in the formation of volcanic shields.

2. Andesitic magma

• Properties: Viscosity and silica concentration at an intermediate level.
• Eruption Style: Can be characterized by explosive activity, resulting in the formation of stratovolcanoes or composite ones.

3. Rhyolitic Magma

Characteristics: Significant viscosity, elevated silica concentration.

• Eruption Typology: extremely violent, frequently resulting in caldera formation.
• Causal factors contributing to volcanic eruptions.
• The timing and manner of eruptions are influenced by several factors, which include:

1. Geological activity

• Volcanoes often develop near tectonic plate borders, where plates intersect, merge, or undergo transformation.
• The motion of these plates can provide circumstances that are favorable for the production and eruption of magma.

2. Accumulation of Pressure

• As magma ascends, it gathers gas (such as water vapor and carbon dioxide), which raises the pressure within volcanic channels.
• An eruption happens when the pressure surpasses the cohesive strength of the surrounding rocks.

3. Temperature fluctuations

• Temperature fluctuations can impact both the melting of adjacent rocks and the viscosity of the magma.
• Hotter magma often exhibits lower viscosity, enabling it to flow more readily.

4. Availability of Water

• The inclusion of water (or other volatile substances) can greatly reduce the melting point of rocks, therefore facilitating the assembly of magma.Furthermore, water vapor is essential in determining the explosiveness of an eruption.
• Geographical dispersion of volcanoes
• The global distribution of volcanoes is uneven, with a major concentration around tectonic plate borders and hotspots.
• An in-depth analysis of their distribution is presented below:

Plate Boundaries

1. Convergent Boundaries

Geographical position: The point of convergence between an oceanic plate and a continental plate.

Illustration: The Cascade Range located in the Pacific Northwest region of the United States.

2. Divergent boundaries

Geographical position: the point at which tectonic plates separate.

At the Mid-Atlantic Ridge, fresh oceanic crust is generated.

3. Transform boundaries

• While often less volcanically active, transform borders have the potential to generate localized eruptions due to the buildup of tension.
• As an illustration, consider the San Andreas Fault.
• Hotspots encompass regions of volcanic activity that occur independently of tectonic plate borders. Notable instances include the Yellowstone Supervolcano and the Hawaiian Islands.

IMAGE SOURCE (THUMBNAIL)