The purpose of this essay is to evaluate the different factors that contribute to the variations in worldwide volcano risks. This analysis will be graded out of 40 marks.
A hazard is a situation that poses a certain level of risk to life, health, property, or the environment. The severity of the hazard differs greatly among different volcanoes. It can range from a mild eruption with minimal consequences and limited damage to a severe and highly dangerous explosion. Although most of the more than sixty volcanoes that erupt each year pose low risks, specific factors can turn a volcano into a significant hazard. This essay aims to examine the factors accountable for these variations.
The main factor to consider when determining the power of an eruption and the shape of a volcano is the viscosity of magma. There are three factors that influence viscosity. Firstly, higher temperatures cause magma density to decrease, making it flow more easily. Secondly, increased dissolved gas in magma decreases its viscosity. Lastly, elevated silica content increases viscosity. Thicker magma with higher viscosity poses a greater risk of explosive eruptions. This type of magma is known as Acid Magma and can be identified by its lower temperature range (600C-1000C), high silica content, and low proportion of dissolved gases. Its consistency is similar to toothpaste, causing blockages and forceful eruptions.
Thick magma eruptions are unpredictable and can have catastrophic consequences for nearby settlements. These settlements are often unprepared for the impact of a violent volcanic eruption. Additionally, explosive eruptions caused by acid magma generate more smoke and ash clouds compared to less explosive eruptions caused by thinner, basic lava. The Eyjafjallajokull volcano in April 2010 created an ash cloud that disrupted European air space, leading to the cancellation of thousands of flights due to safety concerns.
The hazard level of a volcano can be influenced by the type of plate margin it occurs on. Volcanoes located at constructive plate boundaries are typically less violent compared to those at destructive plate boundaries. This is because the magma produced when plates move apart is Basic and has low viscosity, allowing for easy flow. Regular but generally non-explosive eruptions happen from a central vent or fissure. Constructive plate boundaries are often underwater, creating submarine volcanoes like those along the Mid-Atlantic ridge, which pose minimal threats to humans. Therefore, hazards presented by volcanoes at constructive plate boundaries are relatively low. Conversely, at destructive plate boundaries where one plate subducts under another, an acidic magma chamber can form due to intense heat accumulation. Acidic magma has high viscosity and resists flow, resulting in significant pressure buildup that can cause violent and dangerous eruptions involving ash and pyroclastic flow.
This can be a significant danger. Pyroclastic flows are extremely dense and contain toxic gases at very high temperatures. They can also move at speeds over 100km/h. The consequences of such an unpredictable hazard can be extremely serious and potentially life-threatening, especially if there are channels from the erupting volcano leading towards a nearby urban settlement. Additionally, intense eruptions caused by pressure buildup can result in hazards like Tephra and even Lava bombs. Tephra refers to fragments of volcanic rock and lava that are blasted up into the air. These fragments could pose a life-threatening risk to an urban population if they are within reach of the volcano’s tephra ejections. The fact that over 80% of the world’s active volcanoes occur at destructive plate boundaries, including the Pacific Ring of Fire, means that the hazards posed by these volcanoes are very serious due to their explosiveness and unpredictability resulting from the formation of acidic lava there.
The dangers associated with a volcano are influenced by various factors, including the materials expelled during an eruption. When eruptions produce non-explosive basaltic lava flows, the risk to people is generally low, although it can still cause damage to farmland and buildings. However, if there is a crater collapse releasing large quantities of very fluid lava, there is a real danger to people. Nevertheless, the most significant threat occurs during explosive eruptions.
During such eruptions, highly viscous magma results in minimal production of lava that rapidly cools and solidifies. However, these eruptions pose severe hazards due to features like ash clouds, pyroclastic flows, lahars, and tsunamis. An ash cloud can reach a height of 20km within just 30 minutes and be carried hundreds of kilometers away from the volcano’s opening. Tephra from the same eruption typically falls within a few kilometers.
Ash clouds present a notable danger for aircraft as they have caused severe engine damage in several instances over the past 15 years when commercial aircraft unintentionally flew into them. The potential hazard for people aboard these planes is engine failure leading to life-threatening situations.
Volcanic ash not only causes the collapse of buildings and asphyxiation, resulting in death, but it also caused the demise of over 2000 people in Pompeii in 79 AD. Another perilous outcome of explosive eruptions is lahars. Lahars are mudflows composed of volcanic ash and water that can move swiftly through river valleys at speeds ranging from 10 to 100km/h. These cement-like lahars pose a grave threat since they often occur shortly after an eruption when affected individuals are most vulnerable. The eruption of Mount Pinatubo in 1991 claimed many lives due to lahars.
Furthermore, tsunamis present a risk during volcanic eruptions. While submarine volcanoes typically have limited hazards because they are far from populated areas, an eruption at sea can generate a massive wave called a tsunami. Tsunamis pose significant dangers for coastal communities. For instance, the Krakatoa eruption in 1883 triggered waves as high as 35 meters, causing more than 36,000 casualties along the coast of Java and Sumatra alone.
Tsunamis are exceedingly dangerous because they catch affected communities off guard; people don’t perceive themselves to be at risk due to their distance from the volcano.
The hazard level of a volcano is determined by its proximity to population centers. Countries with high population densities and multiple active volcanoes, such as Japan, Indonesia, and the Philippines, put many people at risk. For instance, Naples in Italy has a population of slightly over 1 million and is located just a few kilometers away from Mount Vesuvius. It is clear that volcanoes near populated areas pose greater dangers compared to those in remote regions because they can impact more individuals when they erupt. Unfortunately, limited space often forces people to live in these hazardous locations.
The hazards presented by various volcanoes differ based on two primary factors: the substances expelled and the immediate effects of the volcano, along with its proximity to a populated region. This is because when a volcano is nearer to a densely inhabited area, it has the ability to impact more individuals and consequently brings about a greater danger. This escalated peril arises from the heightened risk it poses to human well-being and life, as well as property and the surrounding ecosystem.
