The Earth has a magnetic field that is generated by electric currents deep in the interior and high above the surface of the planet. The Earth’s core, (2900 km below the surface) experiences radioactive heating and chemical differentiation, the resultant (fluid) convection generates electrical and magnetic energy. The USGS describe it as a naturally occurring, self-sustaining generator where iron in the Earth’s outer core (and magnetic field) induces electric currents which also generate a magnetic field. So there is a loop where the field from fluid motion is sustained by the currents it induces.
The magnetic field also extends far into space where it encounters the moving plasma of the solar wind. The geomagnetic field deflects high energy particles emitted by the Sun as solar wind and shields the Earth’s surface. The Sun’s energy and plasma are dumped into the Earth's upper atmosphere during magnetic storms, these affect satellites, electricity supplies, radio communication and producing expanded auroral displays.
“Geoscience Australia maintains a national network of geomagnetic observatories which forms part of a global observatory network. Data measured at these observatories show how the Earth's magnetic field changes in the Australian region due to processes taking place beneath the Earth's surface, in the upper atmosphere and in the Earth-Sun space environment. These data are used in mathematical models of the geomagnetic field, in resource exploration and exploitation, to monitor space weather, and for scientific research. The resulting information can be used for compass-based navigation, magnetic direction finding, and to help protect communities by mitigating the potential hazards generated by magnetic storms. Geoscience Australia also promotes public safety through the provision of compass and magnetometer calibration services.”
The Earth's magnetic field has both a magnitude (size) and direction. It can be described by combinations of components or ‘elements’. In geomagnetism the elements most commonly referred to are: X, Y, Z, F, H, D and I. Geomagnetic observatories in Australia monitor four of the elements of the geomagnetic field, the true north (X) component, true east (Y) component, vertical (Z) component and the total intensity of the magnetic field (F), the remaining three are calculated. The geomagnetic declination (D), sometimes called magnetic variation, is the angle between true north and magnetic north. The value of magnetic declination should be added to a magnetic compass bearing to yield the true north bearing.
The 'Magnetic Hut’s' is part of one of the Geomagnetic observatories in Australia (see photo). The Hut is used to check 'absolute' magnetic observations weekly with precision instruments like a Declination & Inclination Magnetometer (DIM) comprising an Elsec Type 810 fluxgate unit mounted on a Zeiss 020B theodolite with a Geometrics 816 PPM bought out and placed on top of a solid base.
You may also note the Seismology station just down the road from the Magnetic Hut. The Seismology Station has contained 'variometers' since 1983, in shafts under Towers Hill. These constantly monitor the 4 magnetic parameters listed above and send them to Canberra.
Logging:
Park at the Seismograph or at the base of Towers Hill Road and walk up to the GZ. The earth cache is at this listed location, an inauspicious structure near Towers Hill Road. Observe the Magnetic Hut and read the information above to answer the following questions.
1) That equipment for making absolute observations sounds expensive and is regularly bought out here, where do you think it is placed in the hut?
2) Fill in the missing words. The Earth's magnetic field is generated by ______ _______ deep in the interior and ____ _____ the surface of the planet.
3) How many components (elements) are usually used to describe the magnetic field?
4) Why is the component ’D’ important for navigation?
5) Take and supply a picture from inside the hut with some kind of team identification (name, member or GPSr). Either attach the picture to you log or include it with your answers in the message centre or via email. The message centre can be a bit touchy if you try to add big or multiple files.
Send your answers in the message centre or email and log it online at your leisure, online logs with no answers or doubts over attending the site will be queried and may be deleted. We will try and get back to you in a few days with any queries or the typical answers.
We hope you are drawn to the earthcache about geomagnetism, if you like follow the inserted links or a search engine of your choice to learn about this topic. As well as the golden history of the area and the re-use of mines as bunkers in WW2.