Humans and their properties are usually exposed to natural hazards such as volcanic eruptions directly or indirectly. Natural hazards are dangers arising from geological forces or weather-related occurrences and other examples of such hazards include; earthquakes, floods, tornadoes, and hurricanes. Direct or primary hazards are those related to lava flows; pyroclastic activity, including ash fall, ash flows, and lateral blasts; and the release of gases while indirect or secondary hazards (usually non-volcanic) are those which may be caused by the primary hazards and they include debris flows, mudflows, landslides, floods, and fires.
Causes of volcanic eruptions
Causes of volcanic eruptions are directly related to plate tectonics, and plate boundaries are places where most active volcanoes are located. Plate tectonics is the movement of the outer shell of the earth called plate relative to each other. When a part of the earth's upper mantle or lower crust melts as a result of this plate movement and convection current beneath the earth, magma forms and including a small component of dissolved gases, mostly water vapor and carbon dioxide, are produced. These products generated in the earth’s interior are under pressure and find ways through fissures to the surface and form volcanoes. A volcano is essentially an opening or a vent on earth through which this magma and the dissolved gases it contains are discharged. Magma that has emerged from a volcano onto Earth’s surface is called lava. Eruptions generally occur in sparsely populated areas of the world, causing little or no loss of life or economic damage but when a volcano erupts near a densely populated area, the effects can be disastrous. Millions of people on Earth live close to volcanoes, and as the human population grows, more and more people are living on the flanks, or sides, of active or potentially active volcanoes. In the past century, about 100,000 people have been killed by volcanic eruptions; nearly 23,000 lives were lost in the last two decades of the twentieth century alone. Densely populated countries with many active volcanoes, such as Japan, Mexico, Indonesia and the Philippines are particularly vulnerable. The western United States, including Alaska, Hawaii, and the Pacific Northwest, also have many active or potentially active volcanoes and several of these volcanoes are located near large cities. The advantage volcanic eruptions have on the environment is that it enriches the soil with vitamins. Volcanic ash contains minerals that help the growth of plants. The main reason why scientists study and monitor volcanoes is that people around it should be aware of the hazard. This awareness helps prevents loss of humans and properties when the eruption occurs. Volcanic eruptions can be grouped into two categories: the explosive and the effusive type. This depends on the silica content of the erupting magma which is its basic component. The higher the silica content the more explosive the eruption and the lower the silica content the less explosive the eruption. Mount St. Helene for example is an explosive form of volcanic eruption. This is because before the eruption more gases are stored within the magma chamber (the area within the ground where magma is formed) and during an eruption, the release of these gases that are under pressure can cause enormous damage. They are often accompanied by tremendous earthquake. The population close to this type of eruption is really in danger. The effusive type of eruption occurs when the erupting magma is of low silica content. This type of eruption is the least dangerous and at times serves as spectacles to humans because they can go closer but they may be devastating and may also have global consequences. An example is the Hawai'i jet eruption. The large quantity of dust and ash produced during a volcanic eruption can cause roofs to fall and often smells making air difficult to breath. The lava produced can block roads, burn crops, fall electric poles etc…
Unlike other natural hazards for example earthquakes, it is possible to predict volcanic eruptions since scientists can monitor to tell signs that occur before a volcanic eruption. Things like tiny earthquake, changes in the shape of the mountain, escaping gases, sudden bulge of the ground are signs that a volcanic eruption is likely to occur. Predicting that a volcanic hazard is going to occur gives people time to evacuate in order to reduce the number of casualties. Scientists produce volcanic hazard maps. These maps indicates the type of volcanic hazards expected to occur next and also date how often the eruption is to occur and the probability of its occurring each year. Volcanic monitoring over a long period of time indicates changes before an eruption. Some volcanoes can become dormant or inactive for several years a likelihood of a very explosive eruption. For example, Mount Pinatubo in the Philippines when inactive for about 600 years before erupting explosively in June 1991 while Mount St. Helen before erupting in May 1980 has gone 123 years into dormancy before the catastrophic eruption. The active volcanoes are those that erupt frequently for example, Mauna Loa and Kilauea in the Hawai’i Island. Apart from the psychological adjustment to losses, the primary human adjustment to volcanic activity is just evacuation. People find it difficult to evacuate because of several reasons: they believe because they were born there they cannot leave, others do not want to leave because the soil is fertile, some because of their culture believes it is god’s anger against them so they need to find ways to solve things for example the Mount Pinatubo in Philippine serves as a secrete place where sacrifices are offered. Some do not have a choice because of their limited means.
Reducing death or damage during volcanic eruptions
Getting prepared for a volcanic eruption event can mean the difference between life and death. This may help protect you and your family as well as your properties from volcanic effects as mentioned above. A lot can be done to reduce the negative effects of volcanic eruptions and most obviously is not to build around a volcano even if the soil around volcanoes are fertile as volcanic eruptions do more harm than good to human. This is because this phenomenon becomes a hazard or a disaster when it has direct impact on human and its properties.
Spraying the oncoming lava with sea water is another way of preventing the negative effects of volcanic eruptions; this was proven in 1983 during the Iceland eruption. Scientists believe explosive eruption can cause change in weather. During an explosive eruption, ash clouds sometimes float very high in the air for years, for example, Mount St. Helen produced a lot of ash in the atmosphere which stayed for several months preventing sunlight to get on earth thereby impacting the weather of the area. Volcanic hazards sometimes eject gases such as water vapor, sulfur dioxide, carbon dioxide, carbon monoxide, and hydrogen sulfide. 90% of these gases are mainly water and carbon dioxide. These gases rarely reach populated area but an exception is that of the Lake Nyos disaster in Cameroon in 1986 where about 1700 people suffocated and over 3000 cattle were killed. This was one of the disastrous volcanic gas effects of a volcanic hazard ever registered. Sulfur dioxide in the atmosphere can produce acid rain that incorporate into the soil and plants that are consumed by humans and animals. The reason why scientists study and monitor volcanoes is for those living close to the volcanoes to be aware of volcanic hazards. If you are aware of the risk living close to a volcano, this will help reduce the number of life and property loss during a volcanic eruption. When the scientists have developed a plan, it is important they communicate with the local government and even the general public. The establishment of an emergency plan will help save lives and encourage better land use planning. Below are some key points on how to reduce the negative effects of volcanic eruptions;
Education: The community need to be educated especially those likely to be affected by a volcanic eruption. Government and other natural hazard organizations have to educate the population on how to evacuate if there is an eruption. By doing so the community can quickly and safely get out of danger and less people will be injured. Those living closer to a volcano need to take extra precaution such as providing survival kits that contain food, water, radio, batteries, torch, masks, sturdy shoes, eye protection etc… All these need to be put in the same place so that when need comes to evacuate it will not take a long time. We have to make sure that everyone in the family or those concerned knows where the kit is kept and that they can easily get to it in case of emergency.
Planning: Effects of volcanic eruptions can be very dangerous therefore, it require thorough preparations to be made by those living and working in the vicinity of an active volcano. The eruption might occur suddenly when people are not aware, so it's important to put emergency plans in place. Emergency services can train and prepare the community on how to go about when need comes.The government can plan evacuation tracks to get people out of the area quickly and safely to reduce the number of injuries and death. The number one killer during a volcanic eruption is the ejection of pyroclastic materials and mudflow.
Predicting: Predicting an eruption is going to take place helps evacuate the people in order to reduce the number of deaths and injuries. Hazard Mapping and Satellite Monitoring can tell exactly when an eruption will take place. Before an eruption many things can happen; an eruption most often starts with an earthquake, there is a sudden bulge on the ground, we need to study the behavior of animals and also many gases are often released before an eruption. Several months before Mt. Pinatubo eruptions in 1991, small steam explosions and earthquakes began. Predicting an eruption provides enough time to evacuate the people from danger and death.
Building techniques: Buildings can be constructed that withstand lava flow and ash fall. These buildings can also be prevented by diverting the flow away from these buildings. This will reduce the number of damage which may make people homeless and even unemployed.
Communication device: a communication device is needed such as a radio or a television, to keep updated by the local authorities and make sure you follow them. Also you need to be familiar with evacuation notices and disaster sirens. If during the communication you are not asked to move it is good to take shelter at home. And being at home make sure you take all measure to ensure your security. Only move when you are asked to, because the main cause of death during a hazard is panicking; people do not get confused and are unable to follow instructions.
Charity: Poor countries often receive aid from the government or organizations when affected by volcanic hazards. These aids can be in the form of food, water, money, shelter etc… All these aids help the community concern from hunger and also helps reduce impact.
When an eruption occurs there are some mitigation measures that need to be taken in order to reduce the number of casualties. These include;
Bombing the flow: the government can divert the lava flow by bombing an angle to cause the flow to spread and solidify quickly. Also bombing the flow helps divert the flow from the channel. An alternative is to bomb the vent itself in an attempt to promote lava flow over a wider area; this prevents the formation of lava stream. These people must be trained for the work if not they can cause more harm than good.
Artificial barriers: If the topography is favorable, artificial walls can be used to divert the flow away from the population. This can only be possible for thin fluid flow because behind thick flow there is too much force.
Water sprays: Scientists have conducted studies and publish that approximately 1m3 water is needed to cool 0.7m3 of lava from a temperature of 1100°C to 100°C. This is only possible in areas surrounded with water as the case of Eldjfell eruption in Iceland in 1983 where the pumping rate of water from the adjacent sea of 1m3S-1 chilled 60,000m3 of lava.