What are Volcanic Eruptions?
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The Volcanic eruptions might be a spectacular event to watch but it is really dangerous to encounter one. The volcanic eruptions explode when the lava and the gas are discharged from the volcanic vent. One of the most common consequences of this eruption is the population movements. A large crowd is often forced to flee as the molten lava from the volcano flows. Volcanic eruptions are often caused temporary food shortages and also leads to volcanic ash landslides known as Lahar.
We will know about six basic types of volcanic eruptions which are sure to amaze us. It has different variants and nature which will be worthy to learn.
Six Types of Volcanic Eruptions
In the Volcanic landforms, we have learned the classification of volcanoes by their size and shape. While in this section we will also classify the volcanoes by their eruptive habits. To note, the type of volcanic eruption which occurs plays a prior role in the evolving a volcanic landform, which forms a significant link between the eruptive habit and between the volcanic structure.
Generally speaking, the eruptions can be categorized as being effusive or being explosive.
The Effusive eruptions involve outpouring of the basaltic magma which has a lower viscosity and gaseous content. Explosive eruptions are generally involved with magma and have more viscosity with higher gaseous content. This magma is often broken down into pyroclastic fragments which are caused by explosive gas expansion at the time of expansion.
Based on the eruption behaviour of the volcano, volcanic activity is generally divided into six major types. The types are:
Icelandic
Hawaiian
Strombolian
Vulcanian
Pelean
Plinian
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The Icelandic type is characterized by effusions of molten basaltic lava that flow from long and parallel fissures. After it is cooled down these outpourings get to build into lava plateaus.
The Hawaiian type of volcano eruption is a lot similar to the Icelandic type. In Hawaiian eruption type, however, the fluid lava which flows from the volcano’s summit and the radial fissures to create the shield volcanoes, are very large and have gentle slopes on them.
Strombolian eruptions, yet another type of eruption which involves moderate bursts of the expanding gases, ejects clots of incandescent lava in the cyclical or moreover by continuous small eruptions. These are known as the “lighthouse of the Mediterranean” as they have small frequent outbursts on the Stromboli Island, located on the northeast coast of Italy.
The Vulcanian eruption type is named after the Vulcano Island, located near Stromboli, this eruption generally involves moderate explosions of the gas laden accompanied with volcanic ash. The mixture forms dark, turbulent eruption clouds which rapidly ascend and thus expand in folded shapes.
Next type, Pelean eruption. This type of eruption is associated with explosive outbursts which also release the pyroclastic flows, a dense mixture of the hot volcanic fragments, and the gas that is described as lava, gas, or other hazardous substances. These eruptions are named after the destructive eruption of Mount Pelée which is located on the Caribbean island in the year 1902. The fluids produced by these volcanic eruptions are heavier than air but are of low viscosity and thus pour down from the valleys and sloped with higher velocity. Thus, causing extreme damage.
Last on the list is the Plinian type of eruption which is an intensely violent kind of volcanic eruption that is illustrated by the outburst of Mount Vesuvius in Italy. In this type of volcanic eruption, the gases boiling out of the gas-rich magma produces an enormous and nearly continuous jetting blast.
Fun Fact
1. Some volcanic eruptions are quite explosive while others are spectacular and relatively harmless.
The reason for this out, there are at least four factors .
The number of gaseous constituents dissolved in the magma.
The thickness or the viscosity of the magma coming out.
Rate of decompression of the magma as it proceeds onto the surface.
The number of nucleation sites on which the gases form bubbles.
2. A volcanic eruption occurs when?
When the hot materials from the Earth's interior surface are thrown out from a volcano, eruptions take place. Eruptions can explode from the side branches or the top vent of the volcano. Even there are some eruptions that are very terrible and thus throw out huge amounts of rock and volcanic ash which can kill many people.
FAQs on Types of Volcanic Eruptions
1. What are the main types of volcanic eruptions classified by their explosivity?
Volcanic eruptions are primarily classified based on their explosive character. The main types, ordered from least to most explosive, include:
- Hawaiian: Characterised by the effusive, gentle flow of fluid basaltic lava, creating shield volcanoes.
- Strombolian: Involves distinct, short-lived bursts of thick lava and gas, ejecting volcanic bombs.
- Vulcanian: Features short, powerful explosions of high-viscosity magma, sending large ash clouds high into the atmosphere.
- Plinian: The most violent and catastrophic type, which produces enormous, sustained columns of gas and volcanic ash that can reach the stratosphere.
- Phreatic: A steam-driven explosion that occurs when magma heats groundwater, resulting in an eruption of steam and rock fragments without new lava.
2. What is the fundamental difference between an explosive and an effusive volcanic eruption?
The fundamental difference lies in the magma's properties and how it exits the volcano. An effusive eruption is a relatively calm outpouring of low-viscosity (runny) lava that flows across the ground. In contrast, an explosive eruption is a violent, energetic fragmentation of high-viscosity (thick), gas-rich magma that is blasted into the air as ash and pyroclastic debris.
3. What key factors determine whether a volcanic eruption will be explosive or gentle?
Three primary factors in magma determine the type of eruption:
- Viscosity: This is the magma's resistance to flow. High viscosity (thick magma) traps gases, building pressure that leads to an explosive eruption.
- Gas Content: The amount of dissolved gases like water vapour and carbon dioxide. A high gas content acts like a shaken soda bottle, powering a more explosive eruption.
- Silica Content: The amount of silica in the magma directly controls its viscosity. Magma with high silica content is more viscous and therefore more explosive.
4. How do scientists explain the cause of a phreatic eruption?
A phreatic eruption, also known as a steam-blast eruption, is caused by the interaction between magma and water. It is not driven by the direct explosion of magma. Instead, rising magma heats groundwater or surface water (like a lake or glacier) to an extreme temperature. This causes the water to flash into steam, expanding violently and creating an explosion that blasts through rock, ash, and other debris. No new magma is ejected.
5. Why do different eruption types build volcanoes with different shapes?
The shape of a volcano is a direct result of the type of material it erupts. Explosive eruptions eject thick, high-viscosity lava and ash that solidifies quickly and close to the vent, building up steep-sided, cone-shaped volcanoes (stratovolcanoes). Conversely, effusive eruptions produce fluid, low-viscosity lava that travels far before cooling, forming very broad volcanoes with gentle slopes, known as shield volcanoes.
6. What is the distinction between a volcanic vent and a fissure?
A volcanic vent is a specific, often circular opening at the Earth's surface where volcanic material is emitted, typically located at the summit of a volcano's cone. A fissure, however, is an elongated, linear crack or fracture in the crust from which lava erupts. Fissure eruptions can release vast amounts of lava along the length of the crack, often forming lava plains instead of a single cone.
7. What are pyroclastic flows and why are they considered so dangerous?
Pyroclastic flows are dense, fast-moving avalanches of hot gas, ash, and volcanic rock fragments (pyroclasts) ejected during explosive eruptions. They are considered extremely dangerous because they can race down a volcano's slopes at speeds over 100 km/h and have temperatures of several hundred degrees Celsius. Their combination of extreme heat, high speed, and toxic gases makes them incredibly destructive and impossible to outrun.
8. Can a single volcano produce different types of eruptions over time?
Yes, it is common for a volcano to exhibit different eruptive styles during its active life. Changes in the magma supply, gas content, or composition within the volcano's plumbing system can alter its eruptive behaviour. For example, a volcano might experience a powerful Plinian eruption as it clears its throat, followed by a phase of gentler, effusive lava flows once the initial gas pressure has been released.
