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Comment: 22:48 - 23:44 (00:56)
Source: Annenberg/CPB Resources - Earth Revealed - 13. Volcanism
Keywords: "Andrew Goodliffe", vent, "Mount Katmai", Noverupta, "volcanic ash", pumice, gravity, geophysicist, mass, volcano

Our transcription: The vent in closing Noverupta is largely filled with low density ash and pumice which exerts a weaker pull of gravity than the surrounding rock.
So yet another geophysical property, variations in gravity, may be used to trace the underlying pattern of the rocks.
Well, in a simplified manner there's a mass at the end of a spring inside here, and, well, the spring is extended by the weight of the mass, and that mass will actually be pulled down by the mass underneath in the Earth.
So the greater mass in the Earth, the more the spring will be extended, and basically we measure the extension of the spring in a very precise manner.

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