The area is subjected to frequent earth movements and has a long history of volcanic activity. The mountains have formed as a result of seismic activity. The American coast is part of the North American Plate; the Pacific Ocean to the west lies on the Juan de Fuca plate. The Juan de Fuca plate is subducted below the North American plate. As the subducted Juan de Fuca plate is subjected to increasing pressure it becomes hotter and begins to melt.
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.
It allows us to understand how sedimentary rocks, metamorphic rocks, and Igneous Rocks use one another to not only form the Rock Cycle, but also other processes that are important to our planet. The rock cycle beings with hot magma, deep below the earth’s surface. Once the magma dries, crystallization occurs, and results in igneous rocks. Over time weathering occurs to the igneous rocks. Over time weathering takes over the igneous rocks.
One hazard can often trigger others (e.g. Earthquakes can cause landslides and tsunamis). The San Andreas Fault is a conservative plate boundary that runs 1300km along the Californian coastline. The fracture within the crust, causes crustal instability, between the North American and the Pacific plate. As it traverses, due to convection currents, the tectonic plates are dragged along the entire length of the Californian coast.
Eventually, the friction is overcome and the blocks slip abruptly, releasing pent-up energy with a huge “snap”—an earthquake” (The Plate Tectonic Model – Page 107). Plates diverge at volcanic zones by the ocean basins. These are long huge cracks were lava rises from below and freezes into the Lithosphere (About.com – Geology). In which plates move past each other is call a transform boundary. These are not that common as the converge or diverge plates and the most common one is the San Andreas fault of California [About.com – Geology].
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.
However despite this, as 95% of earthquakes occur on plate boundaries there must be some kind of link between the two and plate tectonic theory can explain this. The theory suggests that the earth’s crust is split into plates which are huge slabs of rock that move due to the convection currents in the mantle. Where two plates meet it causes friction along the plate margin and this creates stresses in the lithosphere and tension in the rock builds overtime. When the strength of the rocks under stress suddenly breaks, they fracture along cracks called faults, sending a series of seismic
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.
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.