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USGS CMG InfoBank: Magnetic Properties of Volcanic Rocks

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Comment: 21:48 - 22:48 (01:00)
Source: Annenberg/CPB Resources - Earth Revealed - 13. Volcanism
Keywords: "Thomas Redfield", magnetism, geophysicist, vent, "magnetic field", temperature, "proton precession magnetometer", "diurnal variation", Noverupta, iron, dome, volcano

Our transcription: Since some rocks are more magnetic than others, geophysicists also map variations in magnetism to help study the subterranean structure of the vent area.
Every rock has some magnetic signature or some magnetic field associated with it that was locked into it at the time of its cooling when it cooled below a certain temperature.
What we do with a proton precession magnetometer is we measure the intensity of everything about you, the magnetic field at that particular point.
And then, with another instrument which is sitting in one place and recording the variations of the Earth's magnetic field, the diurnal variations, the daily variations, we subtract the two, and we are left with a component which we hope is just the rocks themselves.
Magnetic surveying reveals that the area near Noverupta is more magnetic than the surrounding terrain.
The research team believes this results from a concentration of iron rich minerals within and beneath the dome.

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