When parts of the mantle or crust melt, magma is formed. Within these magma chambers, gases in the chambers are causing an increase in pressure. As the pressure gets higher, the magma moves up. It moves up into the “throat” or the volcano, and thus causing an eruption. During some eruptions, you can even see lightning due to ash particles that cause electric sparks.
A volcano is a surface landform resulting from the extrusion of magma from underground as lava, ash, rocks, and gasses are erupted in various proportions. A hazard is something that poses a threat to life, the environment or property. Volcanoes can compromise all these things through the many hazards volcanoes presents. These include lahars, flash flooding, landslides, pyroclastic flows, ash clouds and many others. Each year, around 60 major volcanoes erupt globally.
The nature of an event is initially determined by how the cause was stimulated. Volcanic eruptions occur in many different forms determined by the plate margin they are on. The eruptions on Montserrat 1995 show a strong example of the nature of a volcano at a destructive plate margin. The Soufriere Hills volcano had lay dormant for a long period of time. When the eruption did occur it was seen as explosive as it produced large volumes of acidic lava, ash, pyroclastic flows and steam.
These types of lava are very viscous due to its high silica content. This is because the lava rises from the subduction zone through continental lithosphere which has a low density and is filled with air spaces containing gases which become incorporated into the lava. This very viscous lava often blocks off vents of volcanoes and when the pressure building up in the vent is eventually released, the top of the volcano can be blown off leaving a huge crater, such as in the 2002 eruption of Mount Etna in Sicily. When the two plates involved are oceanic, explosions tend to be less violent than this as the melted lithosphere which forms the lava is denser and so contains fewer gases. At constructive boundaries where plates are moving apart from one another, basaltic lava is erupted between the gaps.
Analyse the factors that cause differences in the hazards posed by volcanoes around the world (40 marks) June 2013 Volcanoes are forms of major extrusive activity and are openings in the Earth’s crust where molten rock and gases reach the surface. The eruption of volcanoes throws out lava, rocks, ash and gases in various proportions. How hazardous a volcano is, depends on a variety of human and physical factors that work in conjunction to determine the level of damage a volcano can have on the human population. The location of a volcano is a large variable which determines the nature of its eruption. Volcanoes are found mainly in three locations, at constructive and destructive plate margins and at hotspots.
The first factor that must be considered is the viscosity of the magma. This can determine how powerful an eruption is and what shape the volcano eventually becomes. Viscosity can be affected by three main factors, firstly, the higher the temperature, the lower the density of the magma, causing it to flow more easily. Secondly, the greater the amount of dissolved gases in the magma, the less viscous it will be, and lastly the higher the silica content, the more viscous it will be. Thicker, more viscous magma has a greater potential for explosive eruptions and therefore represent the greatest potential hazards.
Explain why coastal California is considered a disaster hotspot? (15marks) A disaster hotspot is a country or area that is vulnerable/ disaster prone due the hazards that are; Geophysical, hydro- meteorological. A human factor that increases the risk is vulnerability which includes- population density, wealth and GDP (gross domestic products) which affects the impact of the natural hazard. California is considered a disaster hotspot as all of these factors contribute to an increased danger to human life, meaning it is susceptible to the following natural hazards: earthquake, tsunamis, volcanoes, droughts, wildfires, fog and smog, hurricanes and landslides. One hazard can often trigger others (e.g.
Explain the distribution of the worlds major geophysical hazards Some parts of our planet are more often and more severely afflicted by natural hazards than others. This is due firstly to the geological structure of the Earth and secondly due to climate zones. Earthquakes like the Kashmir, Haiti and New Zealand occur in areas where oceanic plates and continental plates move against each other and collide. The long arc of islands that make up Japan and the stretch of the Andes located inside the coast of Chile are collision zones and therefore more often affected by earthquakes than in Finland, Brazil or Canada. Haiti is on the boundary of the Caribbean and North American plates and is an example of a conservative plate boundary.
AStudy Figure 7 (a) Using Figure 7 and your own knowledge, explain why some places have a high level of landslide and avalanche hazard risk. Landslides and avalanches are one of the world’s major natural hazard type, they cost the US $3.5 billion per year in repair damage. They cause between 25 and 50 deaths in the US each year Hazard: A received natural event which has the potential to threaten both life and property. Landslide: the sliding down of a mass of earth or rock from a mountain or cliff. Avalanche: a mass of snow, ice, and rocks falling rapidly down a mountainside.
Compare and contrast the causes and impacts of two recent Tsunamis in different parts of the world On Sunday the 26th of December 2004 an earthquake, calculated between 9.1 - 9.3 on the Richter scale erupted. This is the third largest earthquake ever recorded. Its epicenter was located off the west coast of Sumatra, Indonesia. This earthquake triggered a Tsunami with maximum wave heights of 30 meters which affected fourteen countries and killed over 230,000 people. 9, 000 of those being foreigners.