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Volcanic Eruptions and Earthquakes

Grade 10
May 10, 2023

Introduction of Volcanic Eruptions and Earthquakes

Disasters are serious disturbances to the functioning of a community that goes beyond its capacity to manage using its own resources. Disasters can be caused by natural, man-made, and technological hazards, and also different factors that influence the exposure and vulnerability of a community.

Naturally occurring physical phenomena is called natural hazard. They can be of various types.

Geophysical hazard: This hazard originates from solid Earth—for example, Earthquakes, landslides, and volcanic Activity.

Hydrological hazard: This hazard is caused by the occurrence, movement, and distribution of water on Earth. For example, Floods and avalanches

Climatological hazard: This type of hazard is related to the climate—for example, Droughts and wildfires.


Meteorological hazard: It is related to weather conditions—for example, Cyclones and storms.

Biological hazard: It is caused by exposure to living organisms and their toxic substances or diseases they may have—for example, Disease epidemics and insect/animal plagues.

Man-made and technological hazards: These hazards are incidents that are caused by humans and occur in or close to human settlements. They consist of complex emergencies, disputes, industrial accidents, transport accidents, environmental degradation, contamination, and pollution. For example, A flood caused by changes in the flow of the river is a natural hazard, while flooding because of a dam failure is a man-made hazard and hence omitted from the National Risk Index.

Natural hazards can also cause secondary natural hazard consequences that produce additional hazards. For example, volcanic Activity can create other hazards, like ash and lava spread.

Natural Hazards
                                                                                                       Natural Hazards

Volcanic Eruptions:

A volcano comprises a deep magma chamber where magma collects, pipes (main vent) that lead to surface vents, and then through vents, lava is emitted in the course of a volcanic eruption. Volcanoes generally have a mountain-like shape. Volcanoes that have not erupted for some time are called dormant volcanoes, and volcanoes that have not erupted, even in the distant past, are called extinct volcanoes. Volcanic Activity and volcanic eruption are usually generated by variations of tectonic plates, causing landslides or earthquakes.


There are various types of volcanic eruptions, such as:

  1. Volcanic eruption:
  2. In this type of eruption, the explosion of steam, water, ash, and rock as magma comes in contact with groundwater or surface water.
  3. Flow volcanic eruption: It contains high-silica lava (>68%).
  4. Basalt flow: It contains low-silica lava (when the amount of silica is low, lava generally has a higher magnesium and iron content).
  5. : It contains fast-moving hot ash, gas, and rock.
  6. Lahar volcanic eruption: It contains mudflow of pyroclastic material into a river valley.
  7. Emission of Carbon dioxide.
Layout of a volcano
                                                                                                   The layout of a volcano

Volcanic eruptions are the most dramatic and fast agents of geologic change. When a volcano erupts, it can expel large amounts of ash and gases into the atmosphere and cover the ground with lots of lava and ash. Volcanic eruptions create new mountains. Large eruptions are very hazardous. Sometimes they kill tens of thousands of people at a time. However, the most dangerous impact of volcanic eruptions is their effect on Earth’s climate.

Earth’s climate results from complex and constantly changing processes and events. The basic source of energy is solar radiation. The inbound solar radiation interacts with the Earth’s surface and atmosphere, so changes to Earth’s surface or atmosphere can impact the climate. For example, the dark lava that flows after eruption absorbs more of the sun’s energy than the soil present in the desert. Therefore, a large amount of lava flow can warm a local area. But a severe impact on climate comes from gases erupted from the volcano that spread and reaches and encircles the Earth’s Planet.

Volcanic Eruptions
                                                                                                       Volcanic Eruptions

Climate Change:

Volcanic eruptions cause a threat to many people. Today there are roughly 500 active volcanoes that are present on Earth, and each year there are 10 to 40 volcanic eruptions occur. Volcanic eruptions produce harmful consequences for the environment, climate, and the health of the exposed persons and are also related to worsening social and economic conditions. Along with magma and steam (water vapor, H2O), the gases that surface in the environment are carbon dioxide (CO2), sulfur dioxide (SO2), carbon monoxide (CO), hydrogen sulfide (H2S), carbon sulfide (CS), carbon disulfide (CS2), hydrogen chloride (HCl), hydrogen (H2), methane (CH4), hydrogen fluoride (HF), hydrogen bromide (HBr) and different organic compounds, and also heavy metals such as mercury, lead, and gold. The unfavorable effects of these gases depend on the distance from a volcanic eruption, the viscosity of the magma, and the concentrations of gas.

Water vapor is the most abundant gas typically erupted. It has been measured to be as high as 97% of gases emitted from some of the volcanic eruptions. However, the water has very little effect on climate because it normally rains out of the atmosphere quite immediately. Therefore, it is very common to find volcanic ash deposits that keep rainfall splash marks.

The greenhouse gas carbon dioxide (CO2) is the second most very common gas (changing from 1% to 50% in various types of volcanic eruptions). Carbon dioxide is heavier than air and hence commonly seen in low-lying areas; it has very adverse effects on plants and animals because it can contaminate and kill animals that breathe it. The CO2 released from volcanic eruptions does not have a significant impact on climate because CO2 from volcanic eruption contribute only about 1% of what is emitted by the burning of fossil fuels. Carbon dioxide released from volcanoes adds to the natural greenhouse effect.

The sulfur dioxide (SO2) gas does not have a noticeable effect on climate. Unlike greenhouse gases, SO2 gas cools the atmosphere. Magma includes a small amount of SO2, usually less than 10% by volume. Large volcanic eruptions push the SO2 gas into the stratosphere (upper atmosphere), where it is carried around the planet. The SO2 gas comes in contact with ample water vapor, and the reaction between SO2 and H2O changes the SO2 gas into sulfuric acid (H2SO4) droplets known as aerosols. These aerosols affect the climate. Each aerosol absorbs some of the solar radiation and hence heats itself and the surrounding upper atmosphere (stratosphere). But each ray of sunlight that strikes an aerosol does not hit the Earth. In the 1900s, there were three huge volcanic eruptions that affected the whole Earth to cool down by as much as 1°C. Volcanic cooling continues for only 2 to 3 years because the aerosols eventually fall out of the upper atmosphere (stratosphere) and enter the lower atmosphere, where rain and wind rapidly scatter them. Sulfate aerosols, too, take part in chemical reactions and form ozone-damaging material.

Climate change
                                                                                                          Climate Change

Human Health Hazards:

Different gases can be released by active volcanoes before, after, or during a volcanic eruption. They can cause various health hazards locally, but they also have the ability to impact the climate globally. There are five main gases that pose a threat to health, they are:

  1. Carbon dioxide (CO2)
  2. Hydrogen chloride (HCl)
  3. Hydrogen fluoride (HF)
  4. Hydrogen sulfide (H2S)
  5. Sulfur dioxide (SO2)

People can get exposed to these harmful volcanic gases either by breathing them in or through contact with the skin and eyes. The impact on health varies from mild to serious, with intermittent deadly exposures. After exposure, people may have difficulty in breathing and the sensation of itchy skin.

Lava flows are flows of magma that come out onto the surface of a volcano. In general, it rarely lava will cause a direct loss of life because it normally flows slowly, and that gives sufficient time for people to be displaced or evacuated. However, it destroys everything that comes in its path through a combination of burial, crushing, and heat. Such volcanic eruptions are also linked with the emission of volcanic gases and aerosols.

Additional impacts are worsening water quality, fewer periods of rain, damage to crops, and damage to vegetation. In volcanic eruptions, the immediate result is increased respiratory system disease and death among those impacted by volcanic eruptions.

Volcanic eruptions can pose multiple health risks depending on the closeness of the volcanic eruption to the community and whether there was any warning.

Volcanic eruptions can cause the following health issues:

  • Choking (suffocation)
  • Infectious diseases like conjunctivitis
  • Eye and skin irritations from acid rain.

Ash and chemicals emitted from volcanic eruption can also develop the risk of food, air, and water contamination. In addition, the deposition of ash on roofs can cause the destruction or collapse of buildings. That may occur immediately or after the event.


The unexpected shaking of the ground that happens when masses of rock change their position below the Earth’s surface is known as an earthquake. The shifting masses send out shock waves that may be powerful enough to change the Earth’s surface, pushing up cliffs and making big cracks in the ground.

Effects of Earthquake:

Social Impacts:

The major effect of earthquakes is the social impact on survivors. However, there are short-term impacts as well as long-term impacts of earthquakes. The short-term effects can be seen in the aftershock of earthquakes. A strong earthquake can devastate buildings, homes, factories, shops, roads, bridges, and schools. These effects cause many people to become homeless.

Moreover, earthquakes can bring about disturbances to transport systems and communication connections. The worst situation can be faced by survivors as they face a lack of drinking water due to the bursting of water pipes and contaminated water supplies. In the cases of long-term social effects, many children become orphans as their parents are killed in the earthquake. Many parents become depressed because their children are killed in schools, colleges, and universities that collapse.


Environmental Impacts:

There are also environmental effects due to earthquakes. For example, A tsunami is produced by an earthquake. Tsunamis are tidal waves that are triggered by the sudden movement of tectonic plates under the seafloor in the course of an underwater earthquake. This tsunami tidal wave can quickly move a long way across the ocean. When a large-scale tsunami (sudden tidal waves) hits the seashore area, it can cause enormous erosion and also damage buildings and roads that come in its path. In the worst situation, even people can also be washed away by the tsunami (underwater earthquake). For example, on 26 December 2004, a tsunami hit Sumatra in the vicinity of the Indian Ocean and caused the deaths of hundreds of thousands of people, animals, etc. Earthquakes can even bring about landslides. It is extremely dangerous, especially for buildings located in unstable areas on hillsides or mountains where soft soils can be easily washed away by the shocks of earthquakes. During an earthquake, people can be buried under the debris of buildings. Many people that are buried alive may die due to metal shocks. There are also aftershock effects of earthquakes. Aftershocks are small earthquakes that scatter to other places, and other people can feel the shocks [tremors] after the main shocks of an earthquake. For instance, when an earthquake happened in Sumatra, it was so high on the Ritcher scale that even Malaysian people living in Penang experienced impacts, though there was no earthquake in Penang.


Economic Impacts:

Other than social and environmental effects, earthquakes also have an adverse effect on a nation’s economy. Governments must take care of the destruction caused by earthquakes. We know that earthquakes cause the destruction of infrastructures, reservoirs, dams, shops, and hospitals. It is the responsibility of the Governments to spend considerable amounts of money to reconstruct the place. Earthquakes also cause the paying off of the capital for distributing food and medicine to sufferers. Investors whose money is blocked in the specific area for development may take the decision to withdraw. When investors withdraw their investment in a specific country, it causes a loss of job openings; due to this, the country’s income declines, which results in an unstable economy.

Effects of earthquake
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Volcanic Eruptions and Earthquakes


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