Analyse the factors that cause differences in the hazards posed by volcanoes around the world (40 marks) Your main factors can be put into two simple categories. Human and physical…..
To what extent can preparedness and planning mitigate the effects of a volcanic hazard (40 marks) Volcanic activity happens across the surface of the globe therefore bringing hazards to every affected area. A hazard is any source of potential damage, harm or adverse health effects. A volcanic hazard is any threat to life and infrastructure due to volcanic activity and related situations such as a landslide near the volcano. Volcanoes can be very dangerous and therefore present many hazards towards both people and land.
They have the ability to kill and destroy, ruining livelihoods and destroying large land masses. The extent of the hazard can differ depending on how prepared an area is for an eruption and how much planning has gone behind minimising the impact. There are many different types of volcanic hazard and each can have different impacts on the economy, society and environment in a region. It is extremely important that disaster reduction measures, such as early warning systems and land use planning, are reinforced to try to reduce these impacts.
There are three main stages to consider when managing a volcano.
The first stage is planning and preparing before the eruption, during its critical period (as it is erupting) and evacuation. Before an eruption there are number of ways to prepare and plan for a volcanic hazard. The most obvious is the prediction of volcanic eruptions, for example, seismic shock waves were used to predict an eruption 48 hours in advance, which resulted in the evacuation of the local population around Popocatepetl, Mexico, in 2000. The development of methods to predict volcanic eruptions is particularly important to provide information for the evacuation of populated regions with around half a billion people now living in the danger zones surrounding the world’s volcanoes. A prediction is a precise statement including the area that will erupt, when it will erupt and the hazards that may arise from the specific eruption. It is easy to locate volcanoes, but it is very difficult to predict exactly when activity will take place, particularly a major eruption therefore meaning it is difficult to prepare or plan for one. There is a very big difference that helps prepare for a volcanic hazard and that is whether you are in a MEDC or a LEDC.
More Economically Developed Countries have the option of monitoring volcanic areas and therefore the potential hazards due to the fact they are able to afford suitable, high quality technological equipment. At the Mount Etna volcano in Catania, Italy they have geo-monitoring programmes which gives volcanologists the ability to monitor and been warned when there are any changes to the volcano such as changes in the chemical balance, any breaking of rocks or further heating up due to ascending magma, extrusive or intrusive activities occurring. This can be operated due to the fact it is an MEDC and the country can therefore afford this options however it may not be an option for many LEDC’s who don’t have the wealth or public education to set up these stations. The Nevado del Ruiz volcano in Columbia demonstrated small scale activity in October 1984 and experts from the US knew the danger that the volcano could pose to the surrounding area if it erupted however they were unable to predict when the main eruption would occur due to the lack of resources and money.
Any small scale activity continued for months and therefore people disregarded any advice including evacuation methods as they thought it was not posing any major threats. MEDC’s on the other hand can greatly reduce the hazards of a volcano in lots of ways. These include creating an exclusion zone around the volcano, being ready and able to evacuate residents and having an emergency supply of basic provisions, such as food. One way of predicting volcanic events is the significance of temperatures around volcanoes rising as activity increases. Thermal imaging techniques and satellite cameras can be used to detect heat around a volcano and this is one way of predicting eruptions to mitigate the effects of the volcano. When a volcano is close to erupting it starts to release gases. The higher the sulphur content of these gases, the closer the volcano is to erupting. Gas samples may be taken and chemical sensors used to measure sulphur levels. The techniques available for predicting and monitoring volcanic activity are becoming increasingly accurate. Volcanoes such as Mount St Helens in the USA and Mount Etna in Italy are closely monitored at all times.
This is because they have been active in recent years and people who live nearby would benefit from early-warning signs of an eruption. However, as well as prediction, people need to be prepared for an eruption. The human race is still not capable of predicting exactly when and where volcanoes and earthquakes will occur. Large scale monitoring of tectonic activity does allow us to narrow down the locations and time frames however, and we monitor volcanoes and earthquakes in many ways. The most widely used method is studying the geographical area of the volcano. For volcanoes scientists can use seismic waves to show if a volcano is getting ready to erupt. Many volcanoes experience an increasing intensity in frequency and size of earthquakes as they prepare to erupt. We can monitor movement- using seismometers which produce seismographs. Volcanic seismicity has three major forms: short-period earthquake, long-period earthquake, and harmonic tremor. Short-period earthquakes are like normal fault-generated earthquakes. They are caused by the breaking and fracturing of brittle rock as magma forces its way upward. Long-period earthquakes indicate increased gas pressure in a volcano’s plumbing system.
Harmonic tremors are often the result of magma pushing against the overlying rock below the surface. Also, ground deformation involves the movement of magma within the lithosphere can deform the ground above, this has been witnessed at Yellowstone beneath Yellowstone Lake. This swelling of the volcano signals that magma has collected near the surface. Scientists monitoring an active volcano will often measure the tilt of the slope and track changes in the rate of swelling. Mount St Helens showed this prior to its eruption in 1980. Both magma movement, changes in gas release and hydrothermal activity can lead to thermal emissivity changes at the volcano’s surface. We can use satellite imagery, activity of minor extrusive features such as geysers and hot springs and mapping to monitor this. Finally, Remote sensing is the use of satellites to detect things about the Earth’s surface. This is useful for monitoring any changes in volcanoes at the surface. Using satellites we can monitor the thermal activity of the volcano to check for upwelling magma, we can check for escaping Sulphur dioxide using gas sensing and we can look to see if the ground is deforming by checking before and after images of the ground.
The satellite can also judge if the ground is being uplifted by measuring the distance between the satellite and the ground. The analysis and study of the previous eruption history of a volcano is important in prediction, along with an understanding of the type of activity produced. At present, research is being conducted to see if it is possible to predict the time of an eruption accurately using the shock waves that are produced as magma approaches the surface, expanding cracks and breaking through other areas of rock. The principal products of volcanic eruptions may be grouped into several broad categories according to the type of material ejected and the transport from the vents to its place of deposition including ash falls, pyroclastic flows, lava flows and gas emissions as well as lahars and ground fractures. Lava flows are less dangerous to human life than to property, traffic, and communication because probable path, of lava flows can be roughly predicted, diversion measures, cool advancing front with water, or disruption of source or advancing front of lava flow by explosives may be taken in principle however the hazards presented may still be dangerous due to the fact highly viscous lava generally does not advance far, but commonly piles, up above an active vent as a lava dome. Such domes can collapse repeatedly and generate dangerous hot block and ash flows and hot surges and blasts.
Kilauea is Hawaii’s youngest volcano and one of the world’s most active. Most eruptions are relatively gentle, sending lava flows downslope from fountains a few metres to a few hundred metres high. Over and over again these eruptions occur, gradually building up the volcano and giving it a gentle, shield-like form. On rare occasions, powerful explosions spread ejecta across the landscape. Such explosions can be lethal, such as the one in 1790 that killed scores of people in a war party near the summit of Kilauea. Due to the fact there is no noticeable pattern and it is hard to predict the extent of the eruptions, it is very hard to plan evacuation methods and protection ideas if the area does not know how hazardous the eruption will be. Poisonous, even lethal, gases can be ejected during the eruption of a volcano or can be released without a triggering eruption. These dangerous gases have been present around eruptions in Lake Nyos. Lake Nyos is an active crater lake that formed by an eruption about 5 centuries ago in North West Cameroon.
Sulphur compounds, chlorine and fluorine react with water to form poisonous acids damaging to the eyes, skin and respiratory systems of animals even in small concentrations. Most volcanic gases are noxious and smell bad, but they can cause mass fatalities. The time available for early warning of gas release is extremely short, and intensified investigation on such gas eruption, as well as keen observation of the respective locations, are absolutely necessary. This means that due to the short warning time, it is very difficult for an area to mitigate the effects of a volcanic hazard as there may not be enough time to plan and prepare for the impacts of an eruption therefore maximising the hazards posed by this type of eruption. The CO2 present in Lake Nyos is dissolved into groundwater and transferred to the lake resulting in the slow saturation of gases. In most crater lakes, turnover of the stratified waters occurs periodically and harmless amounts of dissolved gases are released; however, the problem with Lake Nyos is that it does not periodically turn over so dissolved gases are allowed to reach much higher concentrations. Thirdly, it is important to be prepared for pyroclastic flows and low-density surges that are frequently associated with extremely hazardous types of volcanic eruptions.
Pyroclastic flows consist of a mixture of volcanic gases and ash and are generated during many volcanic eruptions often reaching heats of 900 degrees Celsius. Early warning for this volcanic occurrence is virtually impossible. The only effective method of risk mitigation is evacuation prior to such eruption from areas likely to be affected by pyroclastic flows however as there is not much time to warn people, this means these times of volcanoes are very hazardous as it is only really in MEDC’s where the warning time may be long enough for individuals to escape the impacts. The development of methods to predict volcanic eruptions is extremely important to provide for early evacuation of densely populated regions. Other parts of planning for a volcanic eruption include creating an exclusion zone around the volcano, having an emergency supply of basic provisions and providing or receiving necessary funds needed to deal with the emergency and a good communication system needs to be in place.
Hazard and risk potential of volcanoes can be localised reasonably well, unlike some other types of natural disasters. Reliable predictions can decrease the extent of hazards posed by volcanoes however these predictions are only possible for volcanoes that are well studied and sufficiently instrumented. A prediction based on the statistics of previous eruptions is too vague for specific and short -term prediction of an eruption. A forecast is a general announcement that a volcano will probably erupt in the near future whereas a prediction is a relatively precise statement that describes the part of a volcano that is likely to erupt, the time of the eruption, and the presumable type of eruption. Such predictions must be made public with extreme caution in order to gain trust within the concerned population to ensure they follow preparedness measures In conclusion, preparedness and planning is vital to aid the mitigation of volcanic hazards before an eruption.
Despite this, it is unlikely that people can ever be fully prepared for an eruption and, therefore, it is unlikely to effectively mitigate volcanic hazards. It is very difficult to manage the impacts of volcanic eruptions directly due to the sheer force and unpredictability of volcanoes. There are also extraneous variables which can play an impact, significant or not. Any large scale eruption is always going to pose some type of hazard however smaller scale eruptions can be more easily monitored and therefore mitigated when the eruption takes place. It is very important to impose management strategies and to continually monitor and prepare for volcanic eruptions to avoid any deaths or damage to land in the future.