Volcanic Hazards

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Volcanic Hazards

A volcanic hazard is any volcanic activity or process that poses a threat to human life, livelihoods, and infrastructure. Most of these hazards are harmful and destructive to the area surrounding a volcano, but some are long-reaching and can affect areas hundreds and even thousands of kilometres away from the volcano itself. 

All volcanoes, whether in periods of activity or dormancy, have the capacity to create phenomena that may be harmful and destructive to its surroundings. The first step to reducing the effects of volcanic hazards is to understand a volcano’s patterns and activities. Volcanoes are constantly being observed and studied by scientists. However, this does not mean that all volcanic activity can be anticipated. Volcanoes are natural systems, and therefore always have a level of unpredictability.

Types of Volcanic Hazards

Lava Flows

Lava is a flow of magma that runs down the surface of a volcano. Lava is a hazard that rarely takes the lives of people. It flows slowly, giving residents enough time to flee the surrounding area. However, lava is incredibly destructive, burying, crushing, and burning everything in its path. 

Depending on its composition, lava can vary in viscosity that changes the way it flows. High silica content makes lava viscous, while higher temperatures and water content make it more fluid. High-viscosity andesites typically erupt at temperatures of 700–900°C.  The most fluid of common lava types is low-viscosity basalts. This type usually erupts at 1,100°C–1,200°C. 

Basaltic magma is rich in iron and magnesium and low in silicon. This fluid, hotter magma can flow at great distances. It can form streams, rivers, and spread across the landscape in lobes. On the other hand, andesites rich in silicon don’t travel far from volcanic vents. Andesites rarely erupt. Their flow is short and thick or else builds up into lava domes. Lava domes are unstable and can eventually collapse, creating pyroclastic density currents.

Pyroclastic Density Currents

Pyroclastic density currents are violent phenomena caused by volcanic eruptions. Made of ash, pulverised rock and hot gases, unlike lava, move at incredibly high speeds. This combination of speed, heat, and force make pyroclastic density currents very dangerous to everything around it. Anything in the path of such a devastating force is quickly trampled, crushed, and burned. There is virtually no way of escaping these deadly natural phenomena. 

There are two kinds of pyroclastic density currents: pyroclastic surges and pyroclastic flows. 

Pyroclastic Surges

Pyroclastic surges are watered down, turbulent density currents resulting from the explosive interaction of magma and water. They can travel over topographical features such as valley walls and deposit a thin layer of ash and rock on the areas they touch.

Volcanic hazards include pyroclastic flows, which are surges of watered-down magma, ash, and rock.

Pyroclastic Flows

Pyroclastic flows are fast-travelling, hot density currents of rock, ash, and gas that travel over the ground. Gravity causes pyroclastic flows to run down the sides of a volcano towards the ground below at an average velocity of 70 miles per hour or faster. Pyroclastic flows are forceful and vigorous and have been reported to rush uphill. Their temperatures can fall between 100–600°C. Pyroclastic flows also generate deposits of hot ash and rock near the sides of a volcano. Even after several months, these deposits can maintain temperatures of 400°C.

Fountain collapse pyroclastic flows

This type of pyroclastic flow happens during particularly explosive eruptions. When the mixture of gas and ash is too dense, it isn’t able to rise into the atmosphere. Instead, it collapses around the volcano. 

Dome collapse pyroclastic flows

The second type of pyroclastic flows occurs with the collapse of a lava dome. Domes created from viscous lava can eventually become unstable. Large portions of the dome collapse and come apart, creating a pyroclastic flow. 

Pyroclastic Falls

Also known as volcanic fallout, pyroclastic falls are the products of a volcanic eruption. Tephra is ejected out of a volcanic vent and falls onto the ground. Plinian eruptive columns, volcanic plumes, and ash clouds are common phenomena related to pyroclastic falls.

Tephra/ash fall

In a volcanic eruption, ash and tephra can be sent up into the air at incredible heights. This violent ejection of material contains small, sharp fragments of glass and volcanic rock. Volcanic products, called clasts, can be of various sizes from microns to meters large. Generally, all clasts regardless of their size are called tephra, but volcanic products less than 2mm in size are specified as ash. 

The effects of a tephra fall have many harmful consequences. The fine, abrasive particles can damage machinery and scratch surfaces. Heavier particles can break fragile objects, dent metal, and embed themselves in wood. Pyroclastic falls also contain toxic chemicals that poison local flora and water supplies. Being made of rock, tephra can build up and put a significant strain on buildings. Most especially if it gets wet, an accumulation of tephra can cause the collapse of artificial structures. 

Most tephra will fall in the area surrounding a volcano, but fine volcanic ash can be carried by winds to places hundreds or even thousands of kilometres away. Tephra can build up on roofs, block roads, bury plants, and strip trees of their branches. These have direct consequences on the people living nearby, making travel and agriculture very difficult. 

However, the effects of pyroclastic falls can reach parts of the globe far from the volcanic source. In the case of large volcanic eruptions, eruption clouds can be spread far and wide by the wind. The pyroclastic material in the atmosphere can effectively block sunlight and even cool the Earth’s surface temporarily. 

Lahars

Lahar is a mixture of water, mud, and volcanic debris. This type of mudflow can be caused by a variety of factors that surround an eruption event. In general, however, they all involve the mixing of water with volcanic material. Some factors are the swift melting of snow and ice, large amounts of rainfall on volcanic material, or a volcanic eruption through a crater lake.

Lahar is similar in consistency to wet concrete and flows like a liquid. Gravity allows it to run downhill and over the nearby area’s topography, but it can spread out once it reaches the flat ground. Moving at a pace of 80 kph, it does not flow as fast as pyroclastic flows and other volcanic hazards. However, its dense composition contributes greatly to its destructive capabilities. Lahar either carries away anything in its path or buries it under thick volcanic matter. 

Volcanic Gases

Active volcanoes can emit different gases during and even after an eruption. These gases have the potential to have harmful effects on the health of the people nearby. Volcanic gases can also have significant effects on the global climate. 

The five most hazardous gases from a volcanic eruption are carbon dioxide, hydrogen chloride, hydrogen fluoride, hydrogen sulphide, and sulphur dioxide.

When inhaled or through contact with the eyes and skin, these gases can pose serious threats to the well-being of people. Effects can range from mild to severe, including irritation and difficulty breathing. 

Volcanic gases are invisible, and because they are denser than air they tend to pool in depressions surrounding a volcano. In this manner, they are an especially dangerous volcanic hazard. When converted into sulphate aerosols like sulphuric acid, sulphur gases that reach the stratosphere can cause short-term effects on the climate.

Carbon Dioxide

Carbon dioxide is a component of the air we breathe. However, when volcanoes produce large amounts of carbon dioxide, this gas can displace the oxygen we breathe. Carbon dioxide is heavier than air and can build up in depressions and suffocate the people and animals that end up in these carbon dioxide pockets. Carbon dioxide can dissolve in water and accumulate at the bottom of bodies of water such as lakes. The gas stored in these lakes can later erupt carbon dioxide bubbles and asphyxiate the nearby population. 

Sulfur-based gases

Sulfur-based gases such as sulfur dioxide and hydrogen sulfide can combine with water vapour in the air to create sulfuric acid. Hydrogen sulfide by itself is very acidic and poisonous, even in limited amounts. These acids irritate the tissues in the eyes, nose, throat, and lungs. Large amounts of these sulfur-based gases can also combine with water vapour and form volcanic fog. Breathing this fog is very dangerous, and it can damage the eyes and lungs. 

Fluorine

Compared to the previously mentioned gases, fluorine gas is not as commonly released by volcanoes. However, this yellowish-brown gas is both corrosive and severely poisonous. Fluorine, like carbon dioxide, is denser than air and collects in depressions and low-lying areas. After an eruption, it can also be absorbed into vegetation and poison the food supply for extended periods. The acid hydrogen fluoride is also very harmful to the human body. Contact with this toxic and corrosive acid causes internal burns and destroys calcium in the skeletal system. 

Debris avalanches and landslides

A debris avalanche results from the collapse of a volcano’s unstable slope. Volcanoes with steeper slopes bring forth larger debris avalanches. Debris avalanches can be classified as either hot or cold. A hot debris avalanche is the outcome of volcanic activity. Conversely, a cold debris avalanche is the product of the collapse of an unstable slope. It has been determined that the size of a debris avalanche is proportional to its speed. The more material an avalanche has, the more energy it has stored. 

Landslide is a general term for a gradual mass movement. Landslides happen slower than the sudden movement of debris avalanches.

Both landslide and debris avalanches are common volcanic hazards, however, they are not necessarily the result of volcanic eruptions or volcanic activity. Instead, these two hazards can be caused by factors such as volcanic structural collapse. This is especially likely in areas that usually experience heavy rain. 

Volcanic earthquakes

Volcanic earthquakes are the result of the underground movement of magma. Volcanic earthquakes can produce the same hazards as regular earthquakes. Cracks in the ground, ground deformation, and damage to man-made structures are common effects. Volcanic earthquakes can be categorised into two main types: volcano-tectonic earthquakes and long-period earthquakes.

Volcano-tectonic earthquakes

Volcano-tectonic earthquakes are caused by changes in stress in solid rock due to the introduction or withdrawal of magma. Volcanic earthquakes that fall under this type can result in large ground cracks that cause the ground to subside. These earthquakes are made mainly by the movement of rock to fill in spaces where magma is absent. Volcano-tectonic earthquakes can happen at any moment and are not indicators of a volcanic eruption. 

Long-period earthquakes

Long-period earthquakes are brought about by changes in pressure during the injection of magma into the surrounding rock. The longer it takes for magma to be transported, the more earthquakes are created. Unlike volcano-tectonic earthquakes, long-period earthquakes are indicators of an impending volcanic eruption. Scientists monitor these volcanic tremors in an attempt to warn people in advance of a possible eruption. 

Tsunamis

Tsunamis are massive waves that form after the displacement of large amounts of water. Tsunamis are usually associated with other geological activities such as earthquakes and landslides. However, in some cases, they can also originate from volcanic activity. An underwater eruption, the collapse of large parts of a volcano, or the entry of lahar or pyroclastic density currents into the water can all cause a tsunami. Tsunamis produced by submarine eruptions may only have local effects, however, some explosive eruptions can create great tsunamis that affect whole continents. 

Infamously, the 1883 eruption of the Krakatau volcano in Indonesia caused multiple tsunamis, which took the lives of as many as 36,000 people. Great amounts of pyroclastic flow generated by this eruption displaced the water surrounding the island and led to the creation of tsunami waves.

Jökulhlaups

Jökulhlaup is an Icelandic word that pertains to intense floods of water from glacial lakes or lakes that are situated near a glacier. One possible source for this sudden activity is the eruption of a volcano under a glacier. The strong forces of the volcanic activity melt the ice above or break a dam in the lake. This causes an abrupt release of large volumes of water, producing a flood that can devastate nearby settlements. 

Frequently Asked Questions

What are the primary types of volcanic hazards?

The primary types of volcanic hazards include lava flows, pyroclastic flows (fast-moving clouds of hot ash, rock fragments, and gas), volcanic ash fall, volcanic gases, lahars (mudflows), and volcanic avalanches.

How are volcanic eruptions monitored?

Volcanic eruptions are monitored using various techniques, including seismometers to detect earthquake activity, gas analyzers to measure volcanic gas emissions, ground deformation measurements, and satellite imagery.

Can volcanic eruptions cause climate change?

Large volcanic eruptions can inject significant amounts of ash and sulfur dioxide into the atmosphere, which can lead to short-term cooling of the climate. However, the long-term impact on climate depends on the magnitude and duration of the eruption.

What are the warning signs of an impending volcanic eruption?

Warning signs of an impending volcanic eruption may include increased seismic activity, ground deformation, changes in gas emissions, and the occurrence of small phreatic eruptions (steam-driven explosions).

Can volcanic eruptions occur underwater?

Yes, volcanic eruptions can occur underwater. Submarine volcanoes are volcanic vents located beneath the ocean’s surface, and their eruptions can lead to the formation of new islands or underwater lava flows.

References

1.4 Lahars, jökulhlaups and gasses.(n.d.). Retrieved from OpenLearn.com: https://www.open.edu/openlearn/science-maths-technology/geology/volcanic-hazards/content-section-1.4

Debris Avalanches, Landslides, and Tsunamis. (n.d.). Retrieved from geo.mtu.edu: http://www.geo.mtu.edu/volcanoes/hazards/primer/move.html

Hazardous Volcanic Events. (n.d.). Retrieved from Volcanology.geol.ucsb.edu: https://volcanology.geol.ucsb.edu/hazards.htm

Volcanic Earthquakes. (n.d.). Retrieved from geo.mtu.edu: http://www.geo.mtu.edu/volcanoes/hazards/primer/eq.html

Volcanic Hazards. (n.d.). Retrieved from Geology.com: https://geology.com/volcanoes/volcanic-hazards/

Volcanic Hazards. (n.d.). Retrieved from British Geological Survery: https://www.bgs.ac.uk/discovering-geology/earth-hazards/volcanoes/volcanic-hazards/What are the hazards from volcanoes?.(n.d.). Retrieved from Government of Canada: https://chis.nrcan.gc.ca/volcano-volcan/hazard-risque-en.php

Cite/Link to This Article

  • "Volcanic Hazards". Geography Revision. Accessed on March 28, 2024. https://geography-revision.co.uk/gcse/physical-gcse/volcanic-hazards/.

  • "Volcanic Hazards". Geography Revision, https://geography-revision.co.uk/gcse/physical-gcse/volcanic-hazards/. Accessed 28 March, 2024.

  • Volcanic Hazards. Geography Revision. Retrieved from https://geography-revision.co.uk/gcse/physical-gcse/volcanic-hazards/.