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.
Like the other volcanoes found in the Cascade Range, Mt St Helens (MSH) had been dormant for many years. In March 1980 there were signs of an impending eruption, as several earthquakes occurred. However on the 18th March 1980, an earthquake measuring 5.1 on the Richter Scale rocked the volcano. Within a few seconds of the earthquake, the volcano erupted and the whole northern side of the volcano collapsed causing the largest known landslide in US history. This pulverised rock, glacier ice and ash wiped out all living
NOVA: Volcanoes Volcanoes are landforms where molten rock erupts through the surface of the planet. Think of them as pimples on the face of the earth. Today, there are over 1,500 active volcanoes on earth’s surface. Volcanoes cause serious hazards to not only people, but the environment and the nature around us as well. If an eruption were to occur, a number of life-changing things would happen.
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.
Using the history of eruptions allows us to assess what is likely to happen in the future, for example, in the eruption of Mt. St. Helens in 1980 the volcano erupted on its side from a large bulge this left a huge crater as seen in the image. Because of this deep crater we know that neither a large debris avalanche nor a major lateral blast will like happen again. Mt. St. Helens is a very closely monitored volcano due to its previous eruptions.
Seismicity (or earthquakes) is the shaking of the earth and it is strongly associated with the theory of plate tectonics. Most earthquakes are found on plate margins which are the boundaries between plates. Only 5% of earthquakes that happen every day are not located on plate margins. It has been suggested that human activity could be responsible for some minor earthquakes which do not occur on plate boundaries, for example, the building of large reservoirs puts pressure on the surface of rocks. 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 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.
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].
Geological Survey Unit 4 Shaun Brantley SC300-25 March 27, 2011 The United States Geological Survey provides valuable information as to the potential risks of earthquakes for the entire planet. The USGS is, more or less, an seismological almanac. Earthquakes happen each and every day all over the world but the rumbles are not felt nearly as often as they occur due to their lacking size upon the rector scale. They may not be felt by humans but other species of animals may sense the activity and the data can be recorded by scientists utilizing seismographs. Renditions of seismographs are first recorded to have been used as early as the second century A.D. As science and technology continually advances the scientific community has a greater
This knowledge of plate margins and their movement against one another can help us to understand the distribution of seismic and volcanic events and this is because the majority of events are associated at these plate margins. Wegener’s theory of plate tectonics suggests that all the continents were once joined together in a super continent called Pangea and have since drifted apart due to plate tectonics. To add to this, Sea floor spreading was discovered showing that rock is being created and destroyed, leading us to believe in the existence of plates and plate boundaries. Wegener gained evidence from paleo magnetism and suggested that there were numerous reasons and pieces of evidence for the continents drifting apart. Biologically, there was evidence that proved his theory for example, the Mesosaurus reptile fossils were only found in Africa and South America, proving his ‘jig-saw’ fit idea.