Volcanoes Types, Classification, Causes and Significance

What is a Volcano?

• A volcano is an opening in the earth’s crust through which lava, volcanic ash, and gases escape.
• Volcanic eruptions can happen on land or underwater.

Causes of Volcanism

• Trapped heat: The chemical reactions of the radioactive substances deep within the interior of the earth generate a tremendous amount of heat.
• Temperature gradient: There is a huge difference between the inner layers and the outer layers of the earth due to the differential amount of radioactivity.
• Convectional currents: They are generated in the outer core as well as the mantle due to temperature gradient. Convectional currents in the mantle create convergent and divergent boundaries.
• At the divergent boundary: Molten, semi-molten and sometimes gaseous material appears on Earth usually at the plate margin. The earthquakes may expose fault zones through which magma may escape.
• At the convergent boundary: The subduction of denser plates creates magma at high pressure which will escape to the surface. Because of high pressure, the magma and gases escape with great velocity as the pressure is released through eruptions.

Classification of Volcanoes

Based on the type of eruption:

Shield Volcano

• Lavas low in silica have a low viscosity and have the capacity to flow long distances away from the vent. Over time they develop into gently sloping volcanoes called shield volcanoes.
• For example, Hawaiian island volcanoes like Mauna Loa and Kilauea, Piton de la Fournaise on Reunion Island, and the volcanoes on the Galapagos Islands and in Iceland are shield volcanoes.

Stratovolcano

• More viscous lavas (with a higher silica content) form a steep-sided plug over the vent called a lava dome.
• These volcanoes are made up of layers of pyroclastic materials like ash, lapilli, scoria, and volcanic bombs, and lava, which can have slopes of 30 degrees or more, and are known as stratovolcanoes or composite volcanoes.
• Some examples of stratovolcanoes are Mount Mayon (Philippines) Mount Fuji (Japan), Mount Ruapehu (New Zealand), and Mount Yasur (Vanuatu).

Volcanic Domes

• Opposite to shield volcanoes, volcanic domes are formed when lava is highly-viscous. Because the thick lava can’t travel very far, it starts to pool around the volcano’s vent.
• This can sometimes create a pressure build-up, meaning dome volcanoes are prone to explosive eruptions.

Cinder Cones

• These types of volcanoes typically don’t release lava. Rather, their eruptions typically emit volcanic ash and rocks, known as pyroclastic products.
• Cinder cones are characterized by a bowl-shaped crater at the top, and usually don’t exceed 400m in height.

Based on Frequency of Eruption

Active Volcanoes

• They erupt frequently and are mostly located around the Ring of Fire.
• E.g. Mount Stromboli is an active volcano and it produces so many Gas clouds that it is called the Light house of the Mediterranean.

Dormant Volcano

• These are not extinct but have not erupted in recent history. The dormant volcanoes may erupt in future.
• E.g. Mount Kilimanjaro, located in Tanzania also the highest mountain in Africa is known to be a dormant Volcano.

Extinct or Inactive Volcanoes

• Have not worked in the distant geological past. In most cases, the crater of the Volcano is filled with water making it a lake.
• E.g.: Deccan Traps, India.

Types of Volcanic Eruptions

• Icelandic: It is characterized by effusions of molten basaltic lava that flow from long, parallel fissures. Such outpourings often build lava plateaus.
• Hawaiian: It is similar to the Icelandic variety. In this case, however, fluid lava flows from a volcano’s summit and radial fissures to form shield volcanoes, which are quite large and have gentle slopes.
• Strombolian: These involve moderate bursts of expanding gases that eject clots of incandescent lava in cyclical or nearly continuous small eruptions.
• Vulcanian: It is named for Vulcano Island near Stromboli, generally involving moderate explosions of gas laden with volcanic ash. This mixture forms dark, turbulent eruption clouds that rapidly ascend and expand in convoluted shapes.
• Pelean: It is associated with explosive outbursts that generate pyroclastic flows, dense mixtures of hot volcanic fragments and gas.
  • The fluidized slurries produced by these eruptions are heavier than air but are of low viscosity and pour down valleys and slopes at great velocities. As a result, they are extremely destructive.
• Plinian: This type is an intensely violent kind of volcanic eruption.
  • In this type of eruption, gases boiling out of gas-rich magma generate enormous and nearly continuous jetting blasts that core out the magma conduit and rip it apart.
  • The up rushing gases and volcanic fragments resemble a gigantic rocket blast directed vertically upward.
  • Plinian eruption clouds can rise into the stratosphere and are sometimes continuously produced for several hours.

Significance of Volcanism

• Soil formation: Volcanic materials ultimately break down and weather to form some of the most fertile soils on Earth, cultivation of which has produced abundant food and fostered civilizations.
• Geothermal energy: The internal heat associated with young volcanic systems has been harnessed to produce geothermal energy.
• Minerals: Most of the metallic minerals mined in the world–such as copper, gold, silver, lead, and zinc–are associated with magmas found deep within the roots of extinct volcanoes.

Destructive effects of volcanism

• Volcanism can be a greatly damaging natural disaster. The damage is caused by advancing lava which engulfs whole cities. Habitats and landscapes are destroyed by lava flows.
• Violent earthquakes associated with volcanic activity and mud flows of volcanic ash saturated by heavy rain can bury nearby places.
• Health concerns after a volcanic eruption include infectious disease, respiratory illness, burns, injuries from falls, and vehicle accidents related to the slippery, hazy conditions caused by ash.
• Further effects are the deterioration of water quality, fewer periods of rain, crop damages, and the destruction of vegetation.

Sharing is caring!