Environment

How Do Volcanoes Kill?

Pyroclastic density currents are the biggest killers during volcanic eruptions.

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Volcanoes are much-feared creations of nature known for their ability to kill hundreds to thousands of people, animals, and plants within a matter of moments. Deaths due to volcanoes can be caused due to numerous reasons which have been mentioned below.

1. Pyroclastic Density Current (PDC)

Also known as pyroclastic flow, the PDC is a current of volcanic matter and hot gas moving away from a volcano at high velocity following a volcanic eruption. The PDC can acquire speeds as high as 700 km per hour. The temperature of the gases in the PDCs can exceed 1,000 °C. PDCs usually flow downhill after a volcanic eruption and destroy all that lie on their way including human settlements. While the kinetic energy of the flow flattens trees and buildings, the heat incinerates all living organisms. Thermal injury, asphyxiation, or blast trauma due to PDCs cause death. PDCs are usually too fast for those caught in them to escape. One of the most infamous PDCs was the one that burned the ancient city of Pompeii in Italy. It was so sudden that the people who died hardly had time to react or run towards safety. Given the high velocity and heat, PDCs are the top cause of death during a volcanic eruption. An estimated 59,958 have lost their lives due to PDC from 1500 to 2017 as per data by Statista.

2. Tsunamis

Volcano tsunamis are responsible for the second highest number of fatalities resulting from volcanic action. 56,822 people lost their lives due to volcanic tsunamis from 1500 to 2017 in 23 separate incidents. Such tsunamis can be triggered by violent underwater explosions, caldera collapses, the release of pyroclastic flow in the ocean, volcanic activity related tectonic movements, etc. Massive waves are generated as a result of such events and these waves move at high velocities and crash into land. All that comes in the path of such waves is wiped off into the open sea. About 5% of the tsunamis are caused by volcanic action. One such event happened in Paluweh, Indonesia in 1928 killing 150 people due to volcanic landslide generated tsunami.

3. Lahars

Another extremely destructive volcanic eruption effect is the formation of a lahar. It is basically a violent mudflow or debris flow down the slope of a volcano, usually along a river valley. It is composed a slurry of rocky debris, pyroclastic material, and water. Like PDC, lahars also completely wipe off all that comes in their path. Lahars can kill by asphyxiation by drowning, trauma, or burns. An estimated 49,938 people have died from 1500 to 2017 in 72 incidents involving lahar flows in places with volcanic eruptions. One example of a notable lahar includes that of the Armero tragedy in Tolima, Colombia, on November 13, 1985. The Nevado del Ruiz volcano erupted on this day and melted the mountain’s glaciers. The meltwater and volcanic debris mixed to form four violent lahars that engulfed the town of Amero killing about 20,000 of its inhabitants.

4. Secondary Lahars

A lahar generated after the actual volcanic eruption subsides is called a secondary lahar. Such lahars can occur even years after a volcanic eruption. It can result from avalanches of debris mixed with ice melt or from erosion of fresh, unconsolidated pyroclastic material. Secondary lahars are also highly fatal. 6,377 human deaths due to secondary lahars have been reported from 1500 to 2017 in 41 incidents.

5. Tephra

Tephra refers to any type of rock fragment of any size that is forcibly ejected into the air during a volcanic eruption. Tephra includes scoria, ash, and rock bombs. Tephra can be related to volcanic ballistics as it often travels a parabolic path to land on the ground, objects, of living organisms on its path. Larger rock fragments usually land on the ground closer to the volcano and the smaller ones travel greater distances. When a huge volume of small-sized tephra remains suspended in the atmosphere, it can cause a temporary winter as a microclimate as the tephra reflects back sunlight reaching the atmosphere. Tephra can also be washed down with precipitation to form acid rain or snowfall.

6. Volcanic Avalanches

When volcanic eruptions occur in mountainous regions with large ice caps or glaciers, the collapse of unstable edifices with debris falling on the ice can cause the ice to break away from its position and hurtle down the slopes at high speeds in the form of an avalanche to bury all that lies in its path. Avalanches can also discharge into lakes or the sea generating tsunamis that can result in more fatalities. Volcanic avalanches are the sixth biggest cause of fatalities resulting from volcanic action. 3,525 people are estimated to have been killed in 9 separate incidents between 1500 and 2017.

7. Quiescent Gas

Gases released from volcanoes between eruptions are called quiescent gas. Such gases are usually highly toxic and harmful to health and the environment. Exposure to gases like carbon monoxide, hydrogen sulfide, sulfur dioxide, etc., can kill people instantaneously or over a period of time depending on the type of gas and duration of exposure.

8. Lava Flows

Lava is molten rock that is spewed out by an erupting volcano. Lava can be very fluid or very viscous. Although lava generally moves at a slow speed, fluid lava flows can kill as they move fast and incinerate everything that it touches. Deaths can happen if escape routes are cut off or lava interacts with fuel, vegetation or water to produce a massive fire or explosion.

9. Gas

Massive volumes of toxic volcanic gas are usually given off during a volcanic eruption. These gases can be derived from cavities in volcanic rock, from dissolved volatile substances in magma and lava, or through heated groundwater near volcanoes. These gases are often held responsible for volcano-related deaths as they can be toxic to life on Earth. Volcanic gases can kill by asphyxiation or acidic corrosion.

10. Ballistics

Similar to the ballistics formed during a missile attack, a volcanic eruption can also lead to the formation of ballistics. These are lava and rock fragments having temperatures over 1000 °C hurtling through the air at massive speeds and striking the ground at great distances from the eruption site. The ballistics can have diameters ranging from a few centimeters to tens of meters. Such ballistics can kill or injure any living organism that it strikes including humans. Thus, volcanic ballistics are the third biggest cause of death during volcanic eruptions. 367 known deaths due to ballistics have been reported from 1500 to 2017.

11. Hydrothermal Eruptions

Explosive hydrothermal events also kill during volcanic eruptions. These eruptions generally have localized effects around the vent but on certain occasions, might induce damages further away. Such eruptions involve ejection of boiling water, steam, ballistics, and mud. In 1939, steam explosions in Dieng Volcanic Complex, Indonesia, killed 10 people.

12. Volcanic Lightning

Lightning is common during large volcanic explosive eruptions. The ash clouds formed as a result of such eruptions attract lightning and can be deadly. Only 9 human deaths in 4 separate volcanic lightning events have been reported from 1500 to 2017.

How Do Volcanoes Kill?

RankCause IncidentsFatalities
1PDC10259,958
2Tsunami2356,822
3Lahars7249,938
4Secondary lahars416,377
5Tephra524,315
6Avalance93,525
7Quiescent gas501,698
8Lava flows25659
9Gas16585
10Ballistics57367
11Hydrothermal762
12Lightning49

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