Technological systems and the activities of modern civilization can be affected by changing space-weather conditions. However, it has never been demonstrated that there is a causal relationship between space weather and earthquakes.
Indeed, over Why measure the magnetic field at the Earth's surface? Wouldn't satellites be better suited for space-weather studies? They are not redundant but are instead complementary: Satellites provide good geographical coverage for data collection.
Ground-based magnetometers are much less expensive and much easier to install than satellites. An array of What are the hazards of magnetic storms? Our technology-based infrastructure can be adversely affected by rapid magnetic-field variations. Does the Earth's magnetic field affect human health? The Earth's magnetic field does not directly affect human health.
Humans evolved to live on this planet. High-altitude pilots and astronauts can experience higher levels of radiation during magnetic storms, but the hazard is due to the radiation, not the magnetic field itself. Geomagnetism can also impact the electrically-based technology that we What is declination? At most places on the Earth's surface, the compass doesn't point exactly toward geographic north.
The deviation of the compass from true north is an angle called "declination" or "magnetic declination". It is a quantity that has been a nuisance to navigators for centuries, especially since it varies with both geographic location and time.
Are we about to have a magnetic reversal? Almost certainly not. Since the invention of the magnetometer in the s, the average intensity of the magnetic field at the Earth's surface has decreased by about ten percent.
We know from paleomagnetic records that the intensity of the magnetic field decreases by as much as ninety percent at the Earth's surface during a reversal. But those How does the Earth's core generate a magnetic field? The Earth's outer core is in a state of turbulent convection as the result of radioactive heating and chemical differentiation.
This sets up a process that is a bit like a naturally occurring electrical generator, where the convective kinetic energy is converted to electrical and magnetic energy. Basically, the motion of the electrically Do animals use the magnetic field for orientation? There is evidence that some animals, like sea turtles and salmon, have the ability to sense the Earth's magnetic field although probably not consciously and to use this sense for navigation.
Do any mass extinctions correlate with magnetic reversals? There is no evidence of a correlation between mass extinctions and magnetic pole reversals. Is the Earth a magnet? In a sense, yes. The Earth is composed of layers having different chemical compositions and different physical properties. So we could say that the Earth is, therefore, a " Could magnetic reversals be caused by meteorite or comet impacts? Although extremely unlikely, it might be possible for a reversal of the Earth's magnetic field to be triggered by a meteorite or comet impact, or even for it to be caused by something more "gentle," such as the melting of the polar ice caps.
Are earthquakes associated with variations in the geomagnetic field? Electromagnetic variations have been observed after earthquakes, but despite decades of work, there is no convincing evidence of electromagnetic precursors to earthquakes. It is worth acknowledging that geophysicists would actually love to demonstrate the reality of such precursors, especially if they could be used for reliably predicting Filter Total Items: 6.
Love, Jeffrey J. View Citation. Love, J. Geological Survey Fact Sheet —, 2 p. Year Published: The Boulder magnetic observatory The Boulder magnetic observatory has, since , been operated by the Geomagnetism Program of the U. Geological Survey Open-File Report —, 8 p. Year Published: U. Geological Survey natural hazards science strategy— Promoting the safety, security, and economic well-being of the Nation Executive SummaryThe mission of the U.
Holmes, Robert R. Holmes, R. Geological Survey natural hazards science strategy— Promoting the safety, security, and economic well-being of the Nation: U. Geological Survey Circular —F, 79 p. Year Published: How to build a model illustrating sea-floor spreading and subduction This report describes how to build a model of the outer km miles of the Earth that can be used to develop a better understanding of the principal features of plate tectonics, including sea-floor spreading, the pattern of magnetic stripes frozen into the sea floor, transform faulting, thrust faulting, subduction, and volcanism.
Lahr, J. Year Published: This dynamic earth: the story of plate tectonics In the early s, the emergence of the theory of plate tectonics started a revolution in the earth sciences. Kious, W. To calculate the gradient, and hence the speed, choose distance two points on the best-fit straight line that are some distance apart and find their coordinates.
For example, at a distance of km the age is 63 Ma, and at a distance of km the age is 11 Ma. The gradient of the line is:. The current overall direction of migration of volcanism is towards the southeast, therefore the plate is moving to the northwest. However, prior to about Ma volcanism migrated more or less due south, therefore the Pacific Plate prior to Ma was moving to the north.
By assuming mantle plumes and hot spots are stationary, the motions derived from age progressions such as those along the Hawaii-Emperor Seamount Chain represent true plate motions. However, if the mantle plumes underlying hot spots have also moved with respect to the Earth's axis, but at a rate different from that of plate movement, then the motions defined by a hot-spot trace see Figure 23 may be misleading.
For the Pacific Plate, the Hawaiian hot spot may be the largest hot spot, but it is not the only example of a hot-spot trace on the ocean floor.
Two other examples related to the mantle plumes currently beneath the Cobb and the Macdonald Seamounts are shown in Figure You should be able to appreciate from this figure that both of these chains of seamounts and islands are broadly parallel with the Hawaiian-Emperor Seamount Chain, and the Austral-Marshall Islands Seamount Chain shows a similar bend.
Detailed geochronology of these chains reveals that the age progression along them is also consistent with the rates of northwesterly plate motion derived from the Hawaiian-Emperor Seamount Chain. Since the chances of three and more hot-spot traces moving independently of the plates and one another giving such similar results is remote, these results strongly indicate that hot spots do provide a reference frame within which true plate motions can be measured. This methodology has been extended to studies of numerous hot-spot trails on other plates.
Combined with a knowledge of relative plate motions between adjacent plates, such measurements have allowed the development of a framework of true plate motions across the globe, which are summarised in Figure As you work through this course you will need various resources to help you complete some of the activities.
Making the decision to study can be a big step, which is why you'll want a trusted University. Take a look at all Open University courses. If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module , or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information. Not ready for formal University study?
Then browse over free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released. Every year, thousands of students decide to study with The Open University. Request an Open University prospectus OpenLearn works with other organisations by providing free courses and resources that support our mission of opening up educational opportunities to more people in more places. All rights reserved.
The Open University is authorised and regulated by the Financial Conduct Authority in relation to its secondary activity of credit broking. Skip to main content. Search for free courses, interactives, videos and more! Free learning from The Open University. Featured content. Free courses. All content. Course content. About this free course 15 hours study. Level 2: Intermediate. Course rewards. Free statement of participation on completion of these courses.
Create your free OpenLearn profile. Course content Course content. Plate Tectonics Start this free course now. Free course Plate Tectonics. Box 4 Hawaii Hawaii is part of an extensive chain of islands and submarine volcanic peaks called seamounts stretching almost km across the floor of the Pacific Ocean.
Figure Map showing three of the major seamount and island chains in the Pacific Ocean. The Hawaiian Islands are located at the southeastern end of the Hawaiian Ridge. Question 19 The Hawaii-Emperor chain of islands and seamounts is not straight, but kinked.
Answer If the hot spot is stationary then this must represent a change in direction of the Pacific Plate. Figure 24 Graph of age versus distance from Hawaii measured along the Hawaii-Emperor chain of islands and seamounts.
A best-fit line has been drawn through the data.
0コメント