Distinguish between two chosen hazards in terms of their spatial extent, predictability, frequency, magnitude, duration, speed of onset and effects. [10 marks]
Natural hazards have characteristics that distinguish from one another and two chosen hazards are earthquakes and volcanoes. Earthquakes and volcanoes are related because earthquakes can sometimes lead volcanoes to happen.
As the map shows below, most active volcanoes are located in Ring of fire, the biggest concentration of volcanoes around the edge of the Pacific Ocean, the center of the Atlantic Ocean, the east coast of Africa and in Southern Europe. This is because volcanoes tend to be located near tectonic plate boundaries especially such as destructive and constructive boundaries. However, there are some exceptions like hot spots in the middle of the Pacific Ocean, specifically on the islands of Hawaii. Hot spots are extremely hot and deep regions within the Earth where volcanic activity happens when the mantle rises up and leaks through the crust. Since volcanoes are commonly found on plate boundaries, their spatial distribution is limited. Their distribution is also limited to the areas around the volcanoes, although volcanic ash is able to have potential global impacts such as climate change.
To predict the volcanoes, some methods such as warning signs and monitoring systems can be used despite the fact that they are expensive and hard to exactly pinpoint the specific time and location. Before the volcanic eruptions, there are usually warning signs. For example, the movement of magma leads to small earthquakes, vibrations and swelling of the volcano's slopes. Also, gases will be released near the volcano. On the other hand, some tools will be used to record these warning signs of awakening volcanoes. For instance, Seismographs detects small earthquakes, while tiltmeters and geodimeters measure the swelling of a volcano.
There is no known way of predicting the magnitude, time and place where the earthquake will happen. From the observations, it can be found that earthquakes happen more frequently as population and infrastructure increases. These increase can lead to change in the ground structure which causes the most severe damages. Earthquakes can occur in three different depths; shallow one is less then 60km deep and 300km to 700km is categorized as deep focal depth. Since it takes time for the deep to reach the surface, it doesn't really cause harm. Richter scale is used to measure the size of an earthquake which has a scale of 0.1 to 10. When it is less than 3.5, we can hardly feel it nor it is reported. From 4 to 5, the earthquake only affects the buildings that are poorly built. 5 to 6 affects small regions and causes slight damages. 6 to 7 can affect areas within 100km range. 7 to 8 is considered as major earthquakes and it has serious damge. 8 or greater can cause serious damage up to areas that are 100km far. About 550 volcanoes have erupted in the past. There are dormant volcanoes that have not erupted recently but have erupted in the past 10,000 years. Dormant or not, all volcanoes have potential to erupt again. Every year about 60 volcanoes erupt but the activity of the volcano most of the time is weak while immense eruptions do not happen often. Then magnitude scale is called the Volcanic Exclusivity Index. A volcano's magnitude can range from seven levels. The volume of erupted tephra in level one is small (0.00001 km3). Level two to Level three (0.001km3 - 0.1 km3) is moderate. Level four to level seven is very large (1 km3 - 100 km3 and more). Yellowstone Caldera happened 600,000 years ago but was considered the highest eruption that reached level seven.
The duration of earthquakes can be felt differently depending on how far the observer is from the actual happening of the earthquake. Generally, the length of the fault will determine the size and the duration of the fault and as earthquake spreads, they get weaker. For example, earthquake with a magnitude of 6 can be felt for about 30 seconds whereas the actual duration is short. Seismic waves are the results of earthquake and the velocity tends to depend on depth and range up to 2 ~ 8 km/s on the crust and 13km/s in the mantle. For the volcanoes, they last from few minutes to hours. When volcanoes erupt, the velocities of 200300 m /sec and the speed of lava is slow where it flows a few meters per hour.
Large explosive volcanic eruptions release water vapor, carbon dioxide, hydrogen chloride, surfur dioxide, hydrogen fluoride, and ash onto the Earth's surface. It releases aerosols, which increases the Earth's albedo causing a reflection of radiation to the sun and back up into space. As a result, it cools the Earth's atmosphere and causes a decline in the average temperature. Volcanoes can change the weather. They can cause rain, thunder and lightning. Moreover, they endanger human life and ecosystem. For example, most of the infrastructures such as houses, buildings and roads will be destroyed and animals will lose their habitats near the sites where volcanic eruptions happen.
