Learn about how volcanoes work and the materials they make, volcanic hazards, and famous volcanoes.

Volcanic Eruption Explained

A video by Steven Anderson for TED-Ed. The resources accompanying this video were created by Kylene Richardson and are shared with a CC BY-NC license.

Summary

This video explains how and what can cause volcanic eruptions. It explains why magma is so important, and how the imbalance of the three geological factors (lithostatic pressure, magmastatic pressure, and rock strength) can cause eruptions. It also goes over how plate tectonics weaken rock plates causing volcanoes to form on earth’s surface.

Why Watch This Video?

• Have you ever wondered how volcanoes first formed on Earth?
• Would you like to know how magma contributes to the cause of volcanic eruptions?
• Have you ever been confused by the role plate tectonics play into volcanic eruptions?

Key Terms

Unloading. When a rock’s weight decreases dramatically geological processes such as earthquakes, avalanches, or landslides can remove materials such as rocks or ice. This process lowers the lithostatic pressure and expands the materials. The expansion makes the surface crack upward causing an eruption to happen.

Buoyant force is defined as a pressure that is placed on an object (such as a rock) by a liquid. Pressure is present on all sides of the object but the strongest force is the pressure on the bottom of the object. Buoyant force is especially present whenever an object placed in a liquid floats or sinks.

Hydrothermal alteration is a process that happens when the heat, fluids, and gases inside the magma are too strong for the rock to hold it back. They eat away at the rock, and can slowly cause hard rock to transform into clay. This process essentially lowers or decreases the strength of the rock layer.

Loose Ends

What about all the different types of volcanic eruptions?

The common idea is that when a volcano erupts it’s always the same type of eruption. In reality there are actually four types of volcanic eruptions: Hawai’ian, Strombolian, Vulcanian, and Plinian eruptions.

• Hawai’ian eruptions have the smallest explosions, and lava that erupts is low-viscosity basaltic, meaning it slowly runs down the sides of the volcano.
• Strombolian eruptions are more explosive than the Hawai’ian eruptions and they spill lava less than 100 meters.
• Vulcanian eruptions is the second most explosive eruption, and they spill lava at less than 10km.
• Plinian eruptions is the most explosive type of volcanic eruption. They cause the most shock and damage because this type of eruption spills lava the highest and furthest.

How does plate tectonics affect eruptions?

Tectonic plates are fragments of Earth’s outer shell that shift and move. Most of the world’s volcanoes are located on plate tectonic boundaries (boundaries where plates come in contact with each other). There are three types of boundaries where plate tectonics move: divergent, convergent, and transform. Along divergent boundaries the plates move away from each other. Along convergent boundaries the plates move towards each other. The last type of boundary is transform boundaries where plates move past each other. Volcanoes form at an ocean-to-ocean convergent boundary (where two plates with oceanic crust collide) because along those boundaries, water is added to the mantle, causing partial melting. Volcanoes form in continental rift zones (where continents are splitting into separate plates) because the thinning crust decreases pressure on the hot mantle below, allowing partial melting to happen.

What is a volcano, really?

The common idea about volcanoes is that they erupt on land only, but the truth is that volcanoes can form underwater and erupt there too. A volcano is formed when a hot liquid called magma moves its way towards the surface of the earth. Once it reaches the surface it has to erupt lava, making it a stereotypical volcano. Magma starts developing in a magma chamber and as it begins moving up towards the surface into a vent. Essentially volcanoes are cracks in the earth’s crust that are made of solidified magma and produces lava.

Self-Test

Try these questions to test your understanding.

Volcanoes, Earthquakes, and Plate Boundaries

A video by EBS Documentary. The resources accompanying this video were created by Cameron McFayden for the section on volcanoes (up to the 3:55 mark) and are shared with a CC BY license.

Summary

This video goes over what volcanic activity entails, specifically mentioning the role of the earth’s forces resulting in the movement of magma to the earth’s cracks and weak points and volcanic eruptions. It more importantly describes the types of debris that can be observed through the process of a volcanic eruption such as gases like carbon dioxide, sulphur dioxide and solid debris of pyroclastic material (also known as “fragmented debris called tephra.¹”) Additionally, the video makes a distinction between the differences of lava and magma and what are the various types lava byproducts after it begins to cool.

Why Watch This Video?

• Have you ever wondered what really is thrown into our airways, our waterways and even what comes out of a volcano? Is it just lava and smoke or is their more what scientists would classify as “dangerous” materials coming out of these giant rocks in the ground?
• Would you like to know how the basic process of a volcanic eruption works?
• Have you ever been confused by the idea that volcanoes have been a direct cause to some ice ages that have occurred in the millions of years the earth has been around or how do volcanic eruption cause massive delays at airway centers like we see occasionally on the news?

The best part of this video is that it provides a brief and gentle introduction to all these amazing ideas and questions we all have about volcanoes.

Key Terms

Pyroclastic material is released from a volcano during an eruption and is a mixture of hot, liquid rock formed from magma that is either gently or violently released into the air during a volcanic eruption. A great analogy for this would be with a pop bottle. This analogy states that “The pop bottle analogy illustrates another key point about gas bubbles in fluid, which is that the bubbles can propel fluid. In the same way that shaking a pop bottle to make more bubbles will cause pop to gush out when the bottle is opened, gas bubbles can violently propel lava and other materials from a volcano, creating an explosive eruption¹.”

Molten rock. This type of rock is associated with volcanoes because it is rock that has experienced extreme heat to the point where it melts and has become liquid. These rocks can vary between the content of mineral they include which can change their distinction of magma they make up. For example, basaltic lava (mentioned in the video) is rich in minerals like magnesium and iron and has low amounts of silica resulting in this type of magma. Once this magma reaches the surface during an eruption and begins to cool becoming basalt.

Volcanic ash is a type of debris released in a volcanic eruption and consists of crushed rock, minerals and glass-like particles like obsidian (a hard, glasslike volcanic rock formed when lava cools quickly). This debris is also the smallest type of “fragmented debris called tephra.¹” and is usually smaller than 2 mm in diameter.

Loose Ends

Basaltic, andesitic, and rhyolitic: what’s the difference?

I feel like the video could have gone into more detail on the ideas of basaltic, andesitic and rhyolitic terms for lava origins and why we also use the terms mafic, intermediate and felsic materials to also describe the compositions of the rocks the lava. The reason I say that is that there is more to igneous rocks which are formed out of all types of mafic, intermediate and felsic materials/ elements depending on various conditions of the the process. A simple way to put is worded well in the textbook in Chapter 7.1, How Magma Forms:

Igneous rocks form when melted rock cools. Melted rock originates within Earth as magma.  Magma compositions vary but will have eight main elements in different proportions. The most abundant elements are oxygen and silicon, followed by aluminum, iron, calcium, sodium, magnesium, and potassium. These eight elements are also the most abundant in Earth’s crust.  All magmas have varying proportions of lighter elements such as hydrogen, carbon, and sulfur. Lighter elements are converted into gases like water vapor, carbon dioxide, hydrogen sulfide, and sulfur dioxide as the magma cools.

I feel like this information—though very informative—gives a good summary on how magma forms and differentiates into different types of lava once it erupts from a volcano and then cools as lava instead of going into detail about percentages of silicone dioxide levels as this one factor is misleading to the process of how igneous rocks like basalt and basaltic lava are actually brought into the mind of the viewer without going into extensive detail on what makes basalt, basalt instead of any other type of rock.

Dangers of volcanic ash

The idea that there are different types of solid debris are released during a volcanic eruption besides lava is quite confusing to me and other viewers and as such I believe that this topic on what are implications of this debris affecting our lives needs to be touched on more during the video.

While I believe it would be important for the video to touch on the different sizes of pyroclastic debris released I feel like it would be beneficial to see the video just focus on what happens when volcanic ash is released and what it does to our airways, ecosystems, etc. I feel like if a comparison to normal wood or even fire ash was made it would make the other types of volcanic debris also stand out as way more dangerous than at first glance. For example, National Geographic has an article that explains the dangers even more briefly than the video and summarizes effects to various houses, civilians, animals and plants and adding that info to what the video has already said on airways being shutdown and that volcanic ash hanging in the air can cause major disruptions to climate and the cooling of the earth’s surface:

“Unlike the ash produced by burning wood and other organic materials, volcanic ash can be dangerous. Its particles are very hard and usually have jagged edges. As a result, it can cause eye, nose, and lung irritation, as well as breathing problems. While in the air, ash can cause problems for jet engines, forcing airlines to cancel flights through the affected area. An ashfall that leaves a thick layer of ash may cause roofs to collapse, clog gutters, and interfere with air conditioning units. Animals in an area coated by volcanic ash may have difficulty finding food, as the plants in the region may be covered in ash. Ash can also contaminate water supplies.”

Adding this information would bring awareness to the viewer that volcanic eruptions, no matter how small or big can be dangerous to our environments and that they can cause massive damage to not only property but the entire species of animals and plants.

Shapes of lava flows

Another idea that I feel like that was entirely upon would be that of different shape of lava flows. When I was watching I know the video brought up different forms and ideas of like lava domes from rhyolitic eruptions and gentle runoffs from basaltic eruptions would be the ideas viscosity and how that effects the shapes the lava takes outside of the volcano once it has cooled down. There are various shapes and sizes listed in our own textbook depict such as lava domes mentioned in the video. One good aspect of this is that with additional information such as “highly viscous lava might not flow far at all, and simply accumulate as a bulge, called a lava dome, in a volcano’s crater¹” highly validates what the publisher is trying to get across to the reader and even bringing in examples such as Mt. St. Helens being a great example would help improve the understanding of the video for the audience itself instead of just iterating an idea with no context or concrete example to follow up on this idea.

Self-Test

Try these questions to test your understanding.

References

1. Panchuk, K. (2019, January 18). 11.2 Materials Produced by Volcanic Eruptions. Retrieved November 14^th, 2020.

2. Panchuk, K. (2019, January 18). 7.1 Magma and How It Forms. Retrieved November 15^th, 2020.

3: Brown, T. (2019, April 4). Volcanic Ash. National Geographic. Retrieved November 15^th, 2020.

What Are Volcanic Hazards?

A video by GeoScience Videos. The resources accompanying this video were created by Micaela Gutiérrez and are shared with a CC BY-NC license.

Summary

This video explains what are the principal types of volcanic hazards, their characteristics, how they’re formed and why, what types of volcanoes are associated with each type of hazard, and their consequences. This video also includes various case studies, where examples are provided for further understanding.

Why Watch This Video?

• Have you ever wondered why lava is the most common assumption after a volcano erupts?
• Would you like to know about why lahars are so deadly even though they’re not considered that?
• Have you ever been confused by why different types of volcanic hazards happen with different volcanic eruptions?

Key Terms

Tephra. Material ejected from a volcano to the atmosphere such as ash or lava bombs.

Lahar. Tephra mixed with water (from streams, snow or melting ice) that creates volcanic mudflows or avalanches.

Pyroclastic flow. An extremely chaotic, fast-flowing mixture of volcanic matter, gas, and ash that is extremely hot

Loose Ends

How is a pyroclastic flow formed?

It can be formed in various ways. One way is when volcanic ash is so dense that it falls back to the ground from its upward position. Another way is when lava is chaotically erupted and becomes too steep that makes its dome collapse, so volcanic ash immediately comes out of the volcano going downhill.

What are the three types of tephra?

The first type of tephra is called volcanic ash. It consists of small glass and mineral grains, with particles no more than 2mm. The second type is called lapilli. It consists of small fragments of sizes between 2mm and 64mm. Lapilli has different forms, one of them called Pele’s tears, which form when lava droplets cool rapidly as they “fly” through the air when blasted off the volcano. Chunks of lapilli and ash can also form cinder cones. The third type of tephra is blocks, which form when an explosive eruption shatters the rock of the volcano, blasting those rocks into the air like bombs.

Why does lava flow at different rates (mostly slowly)?

Lava will flow at different rates regarding its temperature, its silica content, its viscosity, and the slope of the land on which it flows. The fewer the silica it contains, the farther it goes.

Self-Test

Try these questions to test your understanding.

Why the Yellowstone Supervolcano Could Be Huge

This video was created and published by the Smithsonian Channel, the YouTube channel owned by the Smithsonian National Museum of Natural History, located in Washington, D.C.

The resources accompanying this video were created by Matthew Woo and are shared with a CC BY license.

Summary

This video introduces the Yellowstone supervolcano, discussing its magnitude, distinctiveness, and the consequences of its past and possible future eruptions. Belonging to a subset of only 12-20 members across the world³, the video describes the rarity of supervolcanoes like Yellowstone, exploring the mechanisms responsible for its volcanism, as well as comparing the scale of its past eruptions against a catastrophic eruption of our own era, specifically that of Mount St. Helens. Through its discussion of Yellowstone’s history, the video highlights the transient, dynamic nature of geological features as they exist, while also showcasing several modern research techniques used in gathering historical data from volcanic systems.

Why Watch This Video?

• Are you interested in why volcanoes erupt, and the events and mechanisms that cause volcanism?
• Have you ever wondered how scientists study past volcanic eruptions and devise models to approximate future ones?
• Are you curious about the effects that such large volcanic eruptions can have on their surrounding regions?

Key Terms

Mantle plume. A rising section, or upwelling, of abnormally hot mantle rock in the Earth’s mantle. Also thought of as “rising columns,”⁶ mantle plumes are thought to originate from the core-mantle boundary, rising through the mantle many times faster, and independently of mantle convection currents. Because of their high temperature, only small increases in temperature are required to liquify them to magma.⁶

Caldera. A large, wide, bowl-like feature caused by a volcanic eruption, and the subsequent collapse of its magma chamber. As magma leaves the chamber during an eruption, the overlying center section of the volcano loses structural support from beneath, collapsing inwards.²

Tephra. A term for the loose material fragments resulting from a volcanic eruption. This includes ash, dust, rock fragments, and even glassy materials, regardless of size or composition.² Often found in distinct layers, the thickness of a tephra layer can be used to approximate the magnitude of a volcanic eruption, and the chemical properties of a given tephra sample can be used to determine its source.⁶

Loose Ends

Are there things we can do to prevent volcanic eruptions before they happen?

Currently, there are no available mechanisms of “stopping” volcanic eruptions, although technology (See Module 7, Text 11.7) has allowed us, through a variety of methods, to detect and forecast imminent eruptions. Much work is being done in this field however, with the goal of slowing down rates of expansion in magma chambers being investigated.⁴ Some proposed models include extensive drilling and pipe systems designed to cool the magma chamber with water, yet such methods also risk interfering with the structural support of the volcano, and possibly triggering an eruption.⁴ As of now, no preventive mechanisms have been proven.

What would the immediate consequences of a Yellowstone eruption look like?

Depending on the magnitude of the eruption, several outcomes could be possible. The United States Geological Survey describes a worst-case scenario resembling that of the eruption 2.1 million years ago, “Such an eruption would produce ash columns that exceed 10 km (6 mi) and cover much of the United States with some ash. Once entering the stratosphere (higher than about 10 km or 6 mi), the ash particles would circle the globe and, in combination with the sulfur dioxide emitted during an eruption, could cause global temperatures to drop.” ¹ The fine particles of this volcanic ash would also have a significant effect both on the lung tissues of air-breathing organisms, and on entire marine ecosystems via the acidic nature of volcanic ash.¹

Can the lengths of time between past eruptions be used in predicting the intervals between future ones?

Yes and no. Had all other influential factors been able to be held constant, time could well be used as a factor in determining when a given volcano would be likely to erupt next. However, such factors are constantly changing, making time a far less useful instrument than other methods currently employed. (See Module 7, Text 11.7) Some of these methods include the monitoring of seismic activity, the measurement of gas escape rates, and measuring the movement in slope, as well as the formation of bulges.² In addition, these methods present a much more reasonable timeframe through which such events can be monitored, as the length of time between eruptions, and the uncertainty associated with such lengths of time are both of enormous magnitude.³

Self-Test

Try these questions to test your understanding.

References

1. Ash and Tephra Hazards from Yellowstone. (n.d.). Retrieved November 07, 2020.

2. Panchuk, K. M. (n.d.). Physical Geology, First University of Saskatchewan Edition. Retrieved November 07, 2020.

3. Questions About Supervolcanoes. (n.d.). Retrieved November 07, 2020.

4. Schmidt, L. J. (2020, November 07). Sensing Remote Volcanoes. Retrieved November 07, 2020.

5. The source of Yellowstone’s heat. (2018, April 16). Retrieved November 07, 2020.

6. Why the Yellowstone Supervolcano Could Be Huge. (2015, June 4). Retrieved November 07, 2020.