Volcano is an opening in a planet or moons crust through which molten rock and gases trapped under the surface erupt, often forming a hill or mountain.

What are the Different Types of Volcanoes?

The term volcano generally refers to an opening of vent in a planets crust from which molten rock ( ash pulverized rock and pumice ) and gases escape from below.

Volcanoes may be classified based on following :

• Frequency of eruption

• Volcanic Features

• Location

Classification based on frequency of eruption

Volcanoes are often classified as :

• ACTIVE

• INACTIVE OR DORMANT

• EXTINCT

Many scientists consider a volcano active if it has erupted within the last 10,000 years. This definition would include approximately 1,500 active volcanoes worldwide.

The second type of volcano is called extinct . They consider a volcano as an extinct volcano if it has not erupted in historical times. However, there are volcanoes that have long been thought to be extinct but suddenly resumed eruption lately. An example of this is FOURPEAKED VOLCANO in ALASKA, which has been considered extinct for 10,000 years but erupted in the 2006.

The term active is used when the volcano is actually erupting or at least showing unusual signs of activity like earthquakes and gas emissions.

What scientists consider as extinct are only those that are not likely to erupt again because their supply of magma has been depleted.

Classification Based on Volcanic Features

A volcano may be a simple crack or opening in the ground from which lava and gases come out.

Mayon Volcano is an example of a stratovolcano

Mayon, also known as Mount Mayon and Mayon Volcano, is an active stratovolcano in the province of Albay in Bicol, Philippines. A popular tourist spot, it is renowned for its "perfect cone" because of its symmetric conical shape, and is regarded as very sacred in Philippine mythology.

This type of volcano probably represent your idea of what a volcano is a tall mountain with a crater on top from which pyroclastic or fire broken materials gases and lava escape it is infact the most common type of volcano.

Shield Volcano

A shield volcano is almost flat and broad like a warriors shield. It's magma has a lower percentage of silica and thus is less viscous than that of a composite volcano and a shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid lava, which travels farther and forms thinner flows than the more viscous lava erupted from a stratovolcano and also 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.

Cinder Cones or Pyroclastic Cones

Cinder Cones are usually small. They are made up of pyroclastic or fragments of volcanic rocks that form steep slopes around their wide crater. They often form in groups near a large volcano. Most of them erupt only once. A well known example of this is Paracutin Volcano in Mexico.

Classification Based on Location

Earth is 70% water and although you may be familiar with continental volcanoes, the land part of earth is only about 30% land. Therefore most of the volcanoes can be found underwater.

Volcanoes that can be found on land are refered to as continental volcanoes. However, there are volcanoes that lie beneath the ocean and high latitude countries like Iceland.

Continental Volcano

A continental volcanic arc forms along the margin of a continent where oceanic crust subducts beneath continental crust. The Cascade Volcanoes are an example. In both cases, the volcanic arc is an active landform. The term complex is used in geology to identify a discrete package of deformed rocks.

Submarine Volcano

Submarine Volcanoes are underneath vents on a certain zones of the ocean floor from which magma can erupt and also submarine volcanoes and volcanic vents are common features on certain zones of the ocean floor. Some are active at the present time and, in shallow water, disclose their presence by blasting steam and rock-debris high above the surface of the sea. Many others lie at such great depths that the tremendous weight of the water above them results in high, confining pressure and prevents the formation and explosive release of steam and gases. Even very large, deep-water eruptions may not disturb the ocean surface.

Subglacial Volcano

Subglacial Volcanoes are located either underneath a glacier itself or under the water, which is inside a glacier and also subglacial volcano, also known as a glaciovolcano, is a volcanic form produced by subglacial eruptions or eruptions beneath the surface of a glacier or ice sheet which is then melted into a lake by the rising lava.

What is Caldera?

A caldera is a large depression formed when a volcano erupts and collapses. During a volcanic eruption, magma present in the magma chamber underneath the volcano is expelled, often forcefully. When the magma chamber empties, the support that the magma had provided inside the chamber disappears.

What Happens when Volcano Erupts?

When a volcano erupts, there may be lava flow poisonous gases, flattened landscape and lowering of atmospheric temperatures. Extremely hot lava destroys everything in it's path. LAHAR, a mudflow that includes all debris along it's path which is usually a river valley is composed of a very thick slurry pyroclastic material, rock debris, water and also Volcanoes spew hot, dangerous gases, ash, lava, and rock that are powerfully destructive. People have died from volcanic blasts. Volcanic eruptions can result in additional threats to health, such as floods, mudslides, power outages, drinking water contamination, and wildfires.

Lava Flow

Lava flow is made up of a molten rock from the volcano, LAHAR is a fast moving flow muddy water with pyroclastic materials from the volcano. Volcanic eruption can shoot out rocks at extremely high speeds that can kill on impact.

Explosions

Massive volcanic explosions are caused by the rapid expansion of gases, which in turn can be triggered by the sudden depressurization of a shallow hydrothermal system or gas-charged magma body or by the rapid mixing of magma with groundwater. The ash, cinders, hot fragments, and bombs thrown out in these explosions are the major products observed in volcanic eruptions around the world. These solid products are classified by size. Volcanic dust is the finest, usually about the consistency of flour. Volcanic ash is also fine but more gritty, with particles up to the size of grains of rice. Cinders, sometimes called scoriae, are the next in size; these coarse fragments can range from 2 mm (0.08 inch) up to about 64 mm (2.5 inches). Fragments larger than 64 mm are called either blocks or bombs. Volcanic blocks are usually older rock broken by the explosive opening of a new vent. Large blocks ejected in such explosions have been hurled as far as 20 km (12 miles) from the vent. Volcanic bombs, in contrast, are generally incandescent and soft during their flight. Some bombs take on strange, twisted shapes as they spin through the air. Others have a cracked and separated crust that has cooled and hardened in flight; they are called “breadcrust bombs.”

Pyroclastic flows

Pyroclastic flows are the most dangerous and destructive aspect of explosive volcanism. Variously called nuées ardentes (“glowing clouds”), glowing avalanches, or ash flows, they occur in many sizes and types, but their common characteristic is a fluidized emulsion of volcanic particles, eruption gases, and entrapped air, resulting in a flow of sufficiently low viscosity to be very mobile and of sufficiently high density to hug the ground surface.

Volcanic Ash

Volcanic ash is abrasive, acidic and odorous. This can eventually cause lung damage in infants, the enderly and those who have resiratory illness. This acidic ash can also damage electrical and mechanical equipment it can also mix with rain and collapse roofs.

Hazard of Volcanic Eruption

When a volcano erupts, its causes great damage to the surrounding area. Its also poses a threat to the lives of people who are living along the slope of a volcano.

Volcanic ash inference with air travel, airplane pilots are adviced to avoid volcanic ash that might be sucked into the jet engines.

Gases

(Water vapor carbon dioxide, sulfur dioxide etc.) spered by the volcano into the atmosphere also have negative impacts, including their effect on the health of people suffering from respiratory problems, global temperature and the formation of acid rain.

Benefits from volcanic eruption

Some people do not have other places to go while other reap the benefits brought by the volcanic eruptions every eruption brings a fresh supply of nutrients to the soil through breakdown and chemical decomposition of rock.

Another beneficial outcome of volcanic eruption is formation of landforms recall that the submarine volcanoes is relatively shallow waters can after several explosions from new island.

There have been volcanic eruption that have happened in the philippines the volcanos involved are mount bulusan in sorsogon mayon volcano in albay and taal volcano in batangas mount bulusan erupted in 2016 while mayon and taal erupted in 2018 and 2020 respectively.

The explosion at restive Bulusan Volcano in Sorsogon province in Bicol on monday affected at least 108,699 people in areas around volcano , explosion affected irosin : 17 barangays , juban: 5 barangays bulan 59 barangay.

The 1984 eruption of Mayon Volcano in Albay Luzon Philipines. An eruption in 1993 caused 79 deaths. Subsequent eruption in 2000, 2014, and 2018 forced tens of thousand of people in nearby villages to evacuate.

As of 12 January 2020 the last eruption from the main crater was 1911 which obliterated the crater floor creating the present lake. In 1965 a huge explosition sliced off a huge part of island moving activity to a new eruption center, Mount Tabaro.

Mount bulusan in sorsogon

Taal Volcano in Batangas

Mayon Volcano in albay

Staying Safe During a Volcanic Eruption

Listen to a local station on a portable battery operated radio or television for updated emergency information and instruction. Local official will give you the most apperance appropriate advice for your particular situation.

Follow any evacuation orders issued by authorities and put your emergency plan into action although it seem safe to stay at home and wait out an eruption if you hazard zone doing so could be very dangerous.

Indoors, close all windows, doors and dampers to keep volcanic ash from entering.

Put all machinery inside a garage or bash to protect it from volcanic ash if buildings are not available cover machinery with large tarps.

Brings animals and livestock into closed shelters to protect them from breathing a volcanic ash.

Gas Clouds

Even beyond the limit of explosive destruction, the hot, ash-laden gas clouds associated with an explosive eruption can scorch vegetation and kill animals and people by suffocation. Gas clouds emitted from fumaroles (volcanic gas vents) or from the sudden overturn of a crater lake may contain suffocating or poisonous gases such as carbon dioxide, carbon monoxide, hydrogen sulfide, and sulfur dioxide. At Lake Nyos, a crater lake in Cameroon, West Africa, more than 1,700 people were killed by a sudden release of carbon dioxide in August 1986. Scientists theorize that carbon dioxide of volcanic origin had been seeping into the lake, perhaps for centuries, and had accumulated in its deep layers. It is thought that some disturbance, such as a large landslide into the lake, could have triggered the outburst of gas, creating an effervescence that stirred the lake and started the degassing.

Ash Falls

Ash falls from continued explosive jetting of fine volcanic particles into high ash clouds generally do not cause any direct fatalities. However, where the ash accumulates more than a few centimetres, collapsing roofs and failure of crops are major secondary hazards. Crop failure can occur over large areas downwind from major ash eruptions, and widespread famine and disease may result, especially in poorly developed countries. In the long run, however, the decomposition of nutrient-rich volcanic fallout is responsible for some of the world’s best soils.

Four of the worst eruptions in history

Since the late 1700s, volcanoes have caused more than 250,000 deaths. Most of these occurred during four disastrous eruptions.

The largest of the four occurred on April 10–11, 1815, at Mount Tambora on Sumbawa Island, now a part of Indonesia. Fifty cubic km (12 cubic miles) of magma were expelled in Plinian ash clouds and pyroclastic flows. Ash layers greater than 1 cm (0.4 inch) thick fell on more than 500,000 square km (193,000 square miles) of Indonesia and the Java Sea. Before the eruption Tambora was a stratovolcano some 4,300 metres (14,100 feet) high; following the eruption, approximately 1,400 metres (4,600 feet) of the summit cone were missing, and in its place was a collapsed caldera 6 by 7 km (3.7 by 4.4 miles) wide and 1 km (0.6 mile) deep. About 10,000 people were killed by the explosive eruption and the tsunamis caused by massive pyroclastic flows entering the sea. Agricultural losses from the thick ash deposits resulted in famine and disease, leading to an additional 82,000 deaths.

Krakatoa (Krakatau) volcano

The second largest eruption of the 19th century also occurred in Indonesia. Krakatoa (Krakatau), a composite volcano on a small uninhabited island between Sumatra and Java, erupted explosively on August 26–27, 1883. The eruption was similar to the Tambora outburst but smaller, involving about 18 cubic km (4.3 cubic miles) of magma erupted in Plinian ash clouds and pyroclastic flows. Krakatoa was a smaller volcano than Tambora, and, when the eruption had emptied part of its magma chamber, it collapsed to form a caldera that was partly below sea level. Twenty-three square km (8.9 square miles) of the island disappeared, and where a volcanic peak 450 metres (1,475 feet) high once stood was water as deep as 275 metres (900 feet). The largest explosion on the morning of August 27 produced an ash cloud that was reported to have reached a height of 80 km (50 miles), and the detonation was heard as far away as Australia. A tsunami over 30 metres (100 feet) high followed the explosion and apparent caldera collapse, killing about 36,000 people on the adjacent shores of Java and Sumatra.

On May 8, 1902, there occurred a violent eruption of Mount Pelée, a stratovolcano on the island of Martinique in the Caribbean Sea. Although less than 1 cubic km (0.24 cubic mile) of magma was erupted, much of it formed a high-velocity pyroclastic flow that swept down a steep valley to the port of Saint-Pierre. Within minutes the town and virtually all of its inhabitants (some 29,000 people) were incinerated.

The second worst volcanic disaster of the 20th century occurred on November 13, 1985, when a relatively small eruption of Mount Ruiz, a stratovolcano in the Andes Mountains of Colombia, killed 25,000 people. This volcano is tall enough, at an elevation of 5,400 metres (17,700 feet), to have a glacial ice cap. When a brief explosive eruption dumped several million cubic metres of hot pyroclastic fragments onto the ice surrounding the summit crater, a sudden surge of meltwater sent massive mudflows down canyons on both the east and west sides of the volcano. Much of the town of Armero, built on a low plain beside the Lagunilla River 50 km (30 miles) east of and nearly 5 km (3 miles) in elevation below the summit of Ruiz, was buried by the mudflows. Twenty-two thousand of its inhabitants were killed.

About 70 percent of the people who died from volcanic eruptions in the past 200 years perished in those four outbursts. The remaining 30 percent were killed in many other less-devastating eruptions. As world population increases, however, so does the risk of greater loss of life from volcanic eruptions. This was made all too clear by the tragedy at Armero. In 1845 a mudflow from Mount Ruiz killed approximately 1,000 people on farms near the site where the town of Armero was later built. In the 1985 mudflow, which was smaller in volume than the 1845 mudflow, more than 20 times as many people were killed.

Volcanism and tectonic activity

Ring of Fire

Taking a more distant view of volcanic landforms from space, one can see that most volcanoes group together to form linear to arcuate belts across Earth’s surface. It is now clear that these volcanic chains are closely related to global tectonic activity. Many active volcanoes are located in the so-called “Ring of Fire” made up of island arcs and mountain ranges bordering the Pacific Ocean (see the map). The concept of seafloor spreading and, more broadly, the theory of plate tectonics offer a logical explanation for the location of most volcanoes.

Tectonic Plate

Tectonic Plate is the scientific theory that explains how the Earth’s lithosphere (a large, solid outer layer) is divided into tectonic plates. These plates move on the Earth’s surface and constantly interact. This process is what creates earthquakes, volcanoes, and mountain ranges.

THANK YOU

The source of this topic is from Grade 9 book and https://www.britannica.com/science/volcano

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