Volcanoes by: Jasmine khabra

Volcanoes are one way the Earth gives birth to itself - Robert Gross

Volcanoes are mountains. But unlike most mountains in the world, formed from folding continental plates, uplift and erosion, volcanoes are created when material from inside the Earth escapes to the surface. When rock from the mantle melts, moves to the surface through the crust, and releases pent-up gases, volcanoes erupt. Extremely high temperature and pressure cause the rock to melt and become liquid rock or magma. When a large body of magma has formed, it rises through the denser rock layers toward Earth's surface.

The 3 types of Volcanoes

Scientists have categorized volcanoes into three main categories: active, dormant, extinct.

Active: Is a volcano that has recently erupted and possibly may erupt again.

Dormant: is a volcano is one which has not erupted in a long time but there is a possibility it can erupt in the future

Lake formed in crater of dormant volcano.

Extinct: in a volcano that erupted thousands of years ago and there's no possibility of eruption

An extinct volcano in Iceland.

Why do Volcanoes erupt?

Volcanoes are a natural way that Earth, and other planets have of cooling of and releasing internal heat and pressure.

Volcanoes erupt because of density and pressure. The lower density of the magma corresponding to the surrounding rocks causes it to rise. It will rise to the surface or to a depth that is influenced by the density of the magma and weight of the rocks above. As magma rise, start to form from the gas dissolved in the magma. The gas bubbles exert prodigious amount of pressure. The pressure helps force the magma to the surface and into the air, sometimes to colossal heights.

Why are Volcanoes in different shapes?

Volcanoes come in different shapes as a result of different types of eruptions and different volcanic materials inside the volcano. Low-silica lava has low viscosity (resistance to flow). Whereas, high-silica lava is more viscous.

High Silica Lava (left) Low Silica Lava (right)

Different types of Lava

Basaltic Lava: Basaltic lava is made with the least amount of silica (compound that occurs as the mineral quartz and as a principal constituent of sandstone and other rocks). Typically, consists of 52% of silica or silicon dioxide (SiO2). It is the fastest and hottest flowing lava, commonly discharged from shield volcano. Can appear as pillow flows when they erupt under water or ice. This allows the flows to build up, creating submarine mountains and islands over time.

Andesitic Lava: It has a higher viscosity than basaltic lava, thus flows at a slower pace. It consists between 52-63% SiO2. Andesitic lava generally produce a small volume that advances no further than the volcanoes base, its flow is described as a block flow. It is common in the Andes Mountains.

Rhyolitic Lava: Has the highest viscosity than any type of lava, and has the greatest content of SiO2. Commonly, consists of over 68% of SiO2. Since it has such a high-silica lava it flows slower than both basaltic and andesitic lava.

Types of Volcanic Rocks

Once the lava has erupted, it cools and solidifies into rock.

Rocks are classified into three groups- ingenous, sedimentary and metamorphic. Ingenous rocks are formed from magma in the Earth's mantel.

Basalt: The Earth's crust is mostly comprised of basalt rocks. It is a heavy, dark, and grainy rock. It is formed at a very high temperature (around 1200ºC), as basaltic lava. When it erupts from a volcano, it is very hot and a liquid. Since we've learned it has a low percentage of silica, it has a high percentage of iron and magnesium, which makes the rock look dark.

Andesite: These kinds of rocks are lighter than basalt because they contain less iron and more silica. It forms from andesitic lava, generally around 800-1000ºC.

Rhyolite: These are very light-colored rocks because it contains a lot of silica and not enough of magnesium or iron. They are formed at lower temperatures between 750-850ºC, and are often thick but quite light.

Basalt (left) Andesite (middle) Rhyolite (right)

Effects of Volcanoes

  • Volcanoes can changes weather. They can cause rain, thunder, and lightning. They have long-term impact on the climate making the world colder.
  • Fast-moving lava can kill people and falling ash can cause difficulty to breathe. They could also die from starvation, fire, and earthquakes which are co-related to volcanoes. People could also lose their possessions as houses, roads, and fields could be destroyed by volcanoes.
  • Lava can kill plants and animals as well.
  • Ash released high in the stratosphere can have negative consequences on the ozone layer.
  • When ash and mud mix with rain and melting snow, it can form lahars. (Lahar is a destructive mud flow on the slopes of a volcano)

An ash covered victim of Indonesia's Mount Merpai volcano eruption arrives at a Yogyakarta hospital


Death toll climbs after major volcanic eruption in Indonesia

Mount Sinabung, Jakartam Idonesia erupted with plumes of ash released more than one mile into the sky. The eruption killed at least 15 people as hot ash of 700 degrees spewed down the mountain slopes in minutes.

Where do Volcano occur?

Active volcanoes typically occur close to major tectonic plate boundaries. Many are also located along the Earth's plate boundaries. Active volcanoes are rare in Australia because there are no plate boundaries on this continent. According to National Geographic, the Ring of Fire, which lies around the Pacific tectonic plate, is home to the most volcanoes and the majority of seismic activity.

How could Volcanoes be good?

Tungurahua ("throat of fire"), an active stratovolcano in Ecuador. Credit: Patrick Taschler

Though volcanoes are known for their destructive power, they play a vital role in adding to the Earth's water supply, provide nutrients to surrounding soil, and creating new islands. According to a Nature Geo science study mentioned in Time Magazine, volcanic eruptions may slow climate change by releasing aerosols which blocks sunlight entering the Earth's stratosphere. Some volcanic eruptions can bring in tourists, proving economic value. Places close to volcanic activity have high potential to receive geothermal energy which can be beneficial to towns and cities.

Most violent eruption in history

On April 10th, 1815, Tambora created one the most powerful eruptions on the planet during the past 10,000 years. The volcano erupted more than 50 cubic kilometers of magma and collapsed afterwards to form a 6 km wide and 1250 m deep caldera. This eruption caused global climate effects and killed over 100,000 people, directly and indirectly. Minor lava domes and flows have extruded on the caldera floor at Tambora during the 19th and 20th century.


Created with images by skeeze - "volcano halema‘uma‘u lava lake sunset"

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