Types of Volcanic Cone

LET US END THIS YEAR WITH A BANG!

Are you having great time with you family this Christmas break? Let's continue our lesson! We are done with the types of magma and lava. We are now going to know about the types of volcanic cone. What now? Let's start. Again, happy holidays.

Do you see a familiar picture above. Yes, you're right. It is the what-we-called the PERFECT CONE VOLCANO. It is the Mayon Volcano located at Albay, Bicol. Is it amazing that this volcano maintains the perfectness of its cone. But do you know what type of volcanic cone Mayon Volcano has?

TYPES of VOLCANIC CONES

These are the major types of volcanic cones:

Major Types of Volcanic Cones

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~ Cinder Cone Volcanoes

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In a cinder cone, lava erupts from a small vent in the crust and 'sprays' melted rock fragments into the air where they then fall back to earth in a pile. These rock fragments are glassy, gas-filled chunks of lava called cinders or scoriathat cool rapidly as they sail through the air and land next to the vent opening, slowly accumulating in the geometric shape of a cone. Some of the most dramatic volcanic eruptions are these displays of lava fountains shooting sparkling, glowing glass-like rock fragments into the air from cinder cones. [1]

A cinder cone or scoria cone is a steep conical hill of loose pyroclastic fragments, such as either volcanic clinkers, cinders, volcanic ash, or scoria that has been built around a volcanic vent. They consist of loose pyroclastic debris formed by explosive eruptions or lava fountains from a single, typically cylindrical, vent. [2]

~ Composite Volcanoes

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A composite volcano is also known as a stratovolcano. These volcanoes form tall, conical shaped mountains. Most of the Earth's active volcanoes have formed a ring around the Pacific Ocean. There are 452 stratovolcanoes in the Pacific Ring of Fire. The volcanoes are located in a volcanic arc on the continental side of subduction zones. [3]

A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic explosive eruptions and effusive eruptions, although some have collapsed craters called calderas. The lava flowing from stratovolcanoes typically cools and hardens before spreading far due to high viscosity. Stratovolcanoes are sometimes called "composite volcanoes" because of their composite layered structure built up from sequential outpourings of eruptive materials. They are among the most common types of volcanoes, in contrast to the less common shield volcanoes. [4]

~ Shield Volcanoes

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A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their low profile, resembling a warrior's shield lying on the ground. This is caused by the highly fluid (low viscosity) lava they erupt which travels farther than lava erupted from stratovolcanoes. This results in the steady accumulation of broad sheets of lava, building up the shield volcano's distinctive form. The shape of shield volcanoes is due to the low viscosity of their mafic lava. [5]

Shield volcanoes are the largest volcanoes on Earth that actually look like volcanoes (i.e. not counting flood basalt flows). The Hawaiian shield volcanoes are the most famous examples. Shield volcanoes are almost exclusively basalt, a type of lava that is very fluid when erupted. For this reason these volcanoes are not steep (you can't pile up a fluid that easily runs downhill). Eruptions at shield volcanoes are only explosive if water somehow gets into the vent, otherwise they are characterized by low-explosivity fountaining that forms cinder cones and spatter cones at the vent, however, 90% of the volcano is lava rather than pyroclastic material. Shield volcanoes are the result of high magma supply rates; the lava is hot and little-changed since the time it was generated. Shield volcanoes are the common product of hotspot volcanism but they can also be found along subduction-related volcanic arcs or all by themselves. [6]

These are the minor types of volcanic cones:

~ Lava Domes

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Lava domes, which may also be referred to as volcanic domes, are common features in volcanic regions throughout the world. Lava domes can come in many shapes and sizes, and while they may not be quite as spectacular as their explosive or flowing counterparts, they are often still an awe inspiring sight to see. The purpose of this page is to provide a brief introduction to lava domes, which will by no means be entirely comprehensive. In fact, even today, there is still much unknown about lava domes and what they can potentially reveal about volcanic systems. [7]

In volcanology, a lava dome or volcanic dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscouslava from a volcano. The geochemistry of lava domes can vary from basalt to rhyolite although most preserved domes tend to have high silica content. The characteristic dome shape is attributed to high viscosity that prevents the lava from flowing very far. This high viscosity can be obtained in two ways: by high levels of silica in the magma, or by degassing of fluid magma. Since viscous basaltic and andesitic domes weather fast and easily break apart by further input of fluid lava, most of the preserved domes have high silica content and consist of rhyolite or dacite. [8]

~ Caldera

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Calderas are some of the most spectacular features on Earth. They are large volcanic craters that form by two different methods: 1) an explosive volcanic eruption; or, 2) collapse of surface rock into an empty magma chamber. [9]

A caldera is a large cauldron-like depression that forms following the evacuation of a magma chamber/reservoir. When large volumes of magma are erupted over a short time, structural support for the crust above the magma chamber is lost. The ground surface then collapses downward into the partially emptied magma chamber, leaving a massive depression at the surface (from one to dozens of kilometers in diameter). Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence and collapse rather than an explosion or impact. [10]

~ Lava Plateaus

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Lava plateaus are extensive areas of flood basalt which are formed by the extensive eruption of basaltic lava over a large area. Rifting of the continental crust is often responsible as the crust thins and allows magma from the mantle to erupt over an extensive area of fissures. The eruptions are often non explosive and continue for a long time building lava flow upon lava flow. [11]

Lava plateaus are formed by highly fluid (runny) basaltic lava during numerous successive eruptions through numerous vents without violent explosions (quiet eruptions). These eruptions are quiet because of low viscosity of lava, so that it is very fluid and contains a small amount of trapped gases. The resulting sheet lava flows may be extruded from linear fissures or rifts or gigantic volcanic eruptions through multiple vents characteristic of the prehistoric era which produced giant flood basalts. Multiple successive and extensive lava flows cover the original landscape to eventually form a plateau, which may contain lava fields, cinder cones, shield volcanoes and other volcanic landforms. In some cases, a lava plateau may be part of a single volcano. [12]