OUR CHANGING WORLD:
Plate Tectonics, Volcanoes & Earthquakes
Code D3: (DVD ONLY)
This DVD contains 3 programs
This program examines the history of the theory of plate tectonics and mechanisms of continental shift that shape the world around us.
In the early twentieth century enough evidence from around the world had been compiled to make some people believe that the world’s continents had not always been at their present location.
The boundaries of continents seemed to match up like a jigsaw puzzle, while similar plants and animals were found in Australia and South America; now separated by ocean. Even mountain ranges and particular strata of rock were found to be continuous from one continent to another.
Led by German thinker Alfred Wegener, the theory of Plate Tectonics gradually developed. This theory held that the earth’s crust is divided into many plates, some oceanic, some continental, that all move independently of each other. Like a skim on milk, the continents are now understood to float on the molten mantle, pushed this way and that by convection currents within the mantle. The lighter plates such as the large, but oceanic Pacific Plate, move as much as 25 mm a year.
When these plates collide or interact the geological fun begins. At some divergent plate boundaries, plates move apart and new mountain ranges are being formed. At other convergent boundaries, two plates collide with one being forced to slide under the other. Still a third form of fault is the transform boundary where two plates slip along side each other. Each of these plate boundaries have the potential to produce volcanoes and earthquakes, but the convergent boundaries that characterise the Pacific’s ‘Ring of Fire’, are the most unpredictable and dangerous.
The process of Plate Tectonics is still under way, albeit very slowly. Inevitably Australia will drift north, the Himalayan Mountains will continue to rise, San Francisco will be on an offshore island and east Africa will also be an island, torn off from the African continent.
This program explores what causes volcanoes, how magma makes its way to the surface and how plate boundaries, subduction zones and hot spots influence their occurrence.
While Australia may only have one active volcano (Big Ben on Heard Island), we are nearby to countries such as Papua New Guinea which rest on the Pacific Ocean’s ‘Ring of Fire’. At places like Rabaul in New Britain, volcanoes are a constant factor of life and only recently new volcanic sea mounts have risen out of the water in the town’s harbour.
Volcanoes can occur at divergent faults between tectonic plates; such as the mid-ocean ridge where new rocks and mountains are being created everyday. This zone circles the globe and includes the island nation of Iceland whose many volcanoes and hot springs are testimony to the volcanic activity created in this zone.
Volcanoes can also occur at subduction zones and many of the Pacific Rim volcanoes fall into this category. Like those at Rabaul, the volcanoes in our region are created when the more-dense Pacific Plate is forced under the less-dense Indo-Australian Plate. As a result, a line of volcanoes such as those at Rabaul is created.
At other places, hotspots are formed in an area of weakness in the earth’s surface, allowing magma to come near to the surface. Yellowstone National Park and the Hawaiian Island chain are both examples of hotspot volcanic activity.
While the volcanoes themselves come in the three major varieties of Shield, Cinder Cone and Composite Volcanoes, the types of explosions that can issue from these volcanoes is varied and depends on many factors. From the super-fast Plinian explosion to the soft rolls of pillow lava that form under water, volcanic eruptions can come in all shapes and sizes.
Due to their size, majesty and destructive powers, volcanoes are frequently studied by vulcanologists, but research into how to predict eruptions is still in its infancy and new discoveries concerning volcanoes are being made everyday.
In 1993 for example, scientists working at mapping the sea floor in the South Pacific Ocean discovered a vast field of volcanoes towering 2,500 metres above the sea floor. Of the 1133 volcanoes mapped, two or three could be erupting at any time and the discovery underlies that we still have much to learn about the processes and mechanisms of volcanoes.
This program is an in-depth look at what causes earthquakes and how we can predict when earthquakes will strike.
Earthquakes are one of the more poorly understood natural disasters that periodically affect people around the world.
Recently in China, Iran, Turkey and many other countries, the devastating effect of earthquakes have been felt. These events can decimate communities and obliterate towns; often towns that have stood impregnable for hundreds of years.
Naturally, due to the appalling loss of life and property caused by earthquakes, a lot of effort has been devoted to understanding how earthquakes occur and how it might be possible to predict the arrival of major earthquakes.
Not until the theory of plate tectonics was advanced did people have any hope of understanding the origins of the enormous amounts of energy seen in earthquakes. Now, with highly accurate instruments, many based in space, seismologists can map the minute movements of the many plates that comprise the earth’s crust.
At the boundaries of these plates several things can happen. If one plate buckles and rises against another plate a normal fault is created and the resulting earthquakes tend to be small. When two plates slide along side each other to create a strike-slip fault, the resulting earthquakes also tend to be small. But when one plate is forced under another in a reverse, or thrust, fault, severe earthquakes can result.
While earthquakes might originate in three major ways, they all have common features such as hypocentres, epicentres and seismic waves. Our knowledge about these features has increased along with the science for recording and mapping the many earthquakes of different magnitude that affect the world each day.
While the science of recording earthquakes is well advanced, the science of predicting earthquakes is a very imprecise science. However, as long as earthquakes continue to be a threat to both life and property, scientists from around the world will work at ways for allowing us to better understand the tremendous forces of earthquakes, and perhaps, to predict or prevent the Big One!
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