‘Evaluate how plate tectonics theory helps our apprehension of the distribution of seismal and volcanic events’ In 1912. Alfred Wegener published his theory that a individual ace continent named Pangaea one time existed about 300 million old ages ago. He proposed that Pangaea so subsequently split into two continents of Laurasia in the North and Gondwanaland in the South and that today’s continents were the consequence of farther splitting of these two land multitudes. Where the home bases split are known as home base boundaries. Wegener’s theory of Continental impetus was supported by both geological and biological grounds that these countries were one time joined. The geological grounds included the stone sequences in Northern Scotland closely holding with those found in East Canada. bespeaking that they were laid down under the same conditions in one location every bit good as the obvious gigue saw fitting visual aspect of today’s continents. in peculiar. the bump of south America adjustment into the indent below West Africa.

The biological grounds comprised of fossil findings associating different continents. Fossil lamp shells found in Indian limestones were comparable with similar dodos in Australia and the dodo remains of Mesosaurus’ were found in both South America and southern Africa. It is improbable that the same reptilian could hold developed in both countries or that it could hold migrated across the Atlantic. Despite the grounds. Wegener’s theory was unable to explicate how Continental motion had occurred. However from the 1940’s extra grounds accumulated after the find of the middle Atlantic ridge and immense pelagic trenches. Examination of the ocean crust either side of the middle Atlantic ridge suggested that sea-floor spreading was happening. Magnetic studies of the ocean floor in the 1950’s. showed regular forms of paleomagnetic striping environing the ridges. It was discovered that when lava erupts on the ocean floor. magnetic spheres within Fe rich minerals in the lava are aligned with the magnetic field of the Earth. This hole as the lava cools and records the earths mutual opposition at the clip of their chilling.

As the mutual opposition of the Earth reverses every 400. 000 old ages. sets of normal and reversed mutual opposition stones are mirrored on either side of the mid ocean ridges. proposing that new stones are being added every bit on either side. Surveys besides established the age of the stones and found immature ages for topographic points on or near the ridges and much older ages for stone nearer to the Continental multitudes. showing that older crust is continually being pushed aside by new crust. The find of sea floor distributing led to the premise that the Earth must be acquiring bigger nevertheless this was non the instance and the find of pelagic trenches allowed for the decision that plates must be being destroyed at different boundaries to suit the addition in their size at mid-oceanic ridges. Hot musca volitanss around the nucleus of the Earth bring forth thermic convection currents within the mantle which cause magma to lift towards the crust and so spread before chilling and sinking.

This circulation of magma is the driving force of plate motion. This motion has an consequence on all the home bases finding their type of boundary each with their ain characteristics and ensuing volcanic and seismal events. Divergent boundaries occur along distributing centres where home bases are traveling apart and new crust is created by magma forcing up from the mantle ensuing in pelagic ridges and rift vales. Where two pelagic home bases are traveling apart they produce mid pelagic ridges with their signifier influenced by the rate at which the home bases separate. Volcanic activity occurs along the ridge organizing pigboat vents which sometimes rise above sea degree suiting reasonably soft sides and often soft eruptions. An illustration of this is located in Surtsey. to the South of Iceland. and Iceland itself. As new crust signifiers and spreads. transform mistakes occur at right angles to the home base boundary due to shearing force per unit area. The parts of the distributing home bases on either side of these mistake lines may travel at different rates doing shallow focal point temblors. Where two Continental home bases are distributing they produce rift vales.

The toffee crust breaks at subdivisions as it moves apart doing a normal mistake where hanging wall falls down comparative to the pes wall due to tensional emphasis. A characteristic of a rift vale is known as a ‘graben’ which forms when a block of stone falls between two mistakes and creates the vale floor and besides a ‘horst’ which is formed when a block of stone is pushed up between two mistakes. This country is associated with volcanic activity as the crust is much thinner than in neighboring countries. Convergent home base boundaries occur when two home bases are traveling towards each other. Where pelagic and Continental crusts meet. the denser pelagic crust is forced under the lighter Continental home base known as subduction. The down warping of the pelagic home base signifiers a really deep ocean trench and the Continental home base border is affected by the contrary mistake lines that cause folding of the home base to bring forth uplifted stone that forms Fold Mountains. As the pelagic crust descends. the addition in force per unit area can trip major temblors along the line of the bomber ducting home base. As it descends further the milieus become hotter and extra heat from the clash causes the stone to run in the benioff zone which begins to lift as batholiths of magma. When they reach the surface they form composite explosive vents.

Volcanic eruptions can besides happen offshore bring forthing volcanic islands referred to as island discharge. Where two types of the same home base meet they create hit zones by which the compaction of the two home bases consequences in the folding of the home base to organize Fold Mountains. As there is small subduction. there is no volcanic activity nevertheless the motion of home bases can trip shallow-focus temblors. Conservative home base boundaries occur when two crustal home bases slide past each other and the motion of the home bases is parallel to the home base boundary. The motion of the home bases creates emphasiss between the home base borders and as they rub past each other the release of clash triggers shallow focal point temblors. However as there is no subduction. there is no volcanic activity. The best known illustration of a conservative boundary is the San Andreas Fault in California. where the Pacific and North American home bases move parallel to each other.

Volcanic activity that does non happen along any home base boundary can be the consequence of many a mistake lines and hot musca volitanss beneath the crust. Alfred Wegener’s theory allowed us to derive penetration into the possible creative activity of our tectonic home bases and their boundaries. The grounds provided by wegener’s theory and the record of paleo-magnetism upon the ocean floor supported the thought that the tectonic home bases are traveling. Supported by the theory of convection currents. the motion of these home bases helps our apprehension of the distribution of seismal and volcanic events by leting us to place changing home base boundaries that create different characteristics and as a consequence cause these events. This explains their distribution. as events such as these are located in countries above home base boundaries. apart from the uneven one which can happen above many a mistake lines or hot musca volitanss caused by the motion of home bases.