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.
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
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.
The movement of the plates is divided in three ways: they move together (converge), the move apart (diverge), or they move past each other [About.com – Geology]. “Earthquakes occur along faults, where huge blocks of rock are grinding past each other. Tectonic motions produce directional pressure, which causes rocks on either side of a large fracture to move past each other. The movement is rarely smooth; usually the blocks stick because of friction, which slows their movement. 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).
As a result of this earthquake theories such as, elastic-rebound has been one of the models used to portray the earthquake cycle. Although, there is no actual set answer for the magnitude of the San Francisco Earthquake some say it was 7.7 however, it was re-evaluated and was said to be 7.9. At the surface of California's plains the offset was about 20 feet and was monitored near Point Reyes. However, a study done has found that the measurements were approximately 24 feet near Point Reyes and 28 feet close to Shelter Cove (north of the rupture). The main area hit was San Francisco yet, it did affect almost all of the San Andrea’s Fault.
What did Harry Hess propose in 1963? He proposed that molten rock erupts from the Earth's interior along mid-oceanic ridges, creating new seafloor. What magnetic field, polarity evidence supports the theory of plate tectonics? -the earth's magnetic field was especially strong over the oceanic ridges that were made up of iron rich materials -the magnetic field formed a zebra-striped
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.
This earthquake occurred on the Denali-Totschunda fault system – one of the longest strike-slip faults in the world. The tectonic setting of this area results from the interaction of the Pacific plate (oceanic) and the North American plate (Continental). This results in the subduction of the Pacific plate beneath the N.American plate because the continental plate is thicker and less dense and sudden movements in this subduction results in an earthquake such as the one experienced in Denali in 2002. This earthquake measured 7.9 on the Richter scale and violent shaking of the ground triggered many landslides which buried valleys and glaciers. The one service that was damaged the most was the Northway airport – this was the effect of ‘liquefaction’ caused by the rupture transforming water saturated sediments into a liquid slurry.
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.
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