Gravity Changes and Internal Processes: Some Results Obtained from Observations at Three Volcanoes |
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| Authors: | Email author" target="_blank">Gerhard?JentzschEmail author Adelheid?Weise Carlos?Rey Carl?Gerstenecker |
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| Institution: | (1) Institut für Geowissenschaften, Friedrich-Schiller Universität, Burgweg 11, D-07749 Jena, Germany;(2) INGEOMINAS (Instituto de Investigationes en Geosciencias, Mineria y Quimica), Diagonal 53 No. 34-53, Santafe de Bogota, Colombia;(3) Institut für Physikalische Geodäsie, Technische Universität Darmstadt, Petersenstr. 13, D-64287 Darmstadt, Germany |
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| Abstract: | Temporal gravity changes provide information about mass and/or density variations within and below the volcano edifice. Three active volcanoes have been under investigation; each of them related to a plate boundary: Mayon/Luzon/Philippines, Merapi/Java/Indonesia, and Galeras/Colombia. The observed gravity changes are smaller than previously expected but significant. For the three volcanoes under investigation, and within the observation period, mainly the increase of gravity is observed, ranging from 1,000 nm–2 to 1,600 nms–2. Unexpectedly, the gravity increase is confined to a rather small area with radii of 5 to 8 km around the summit. At Mayon and Merapi the parallel GPS measurements yield no significant elevation changes. This is crucial for the interpretation, as the internal pressure variations do not lead to significant deformation at the surface. Thus the classical Mogi-model for a shallow extending magma reservoir cannot apply. To confine the possible models, the attraction due to changes of groundwater level or soil moisture is estimated along the slope of Merapi exemplarily by 2-D modelling. Mass redistribution or density changes were evaluated within the vent as well as deeper fluid processes to explain the gravity variations; the results are compared to the model incorporating the additional effect of elastic deformation. |
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| Keywords: | Gravity changes at volcanoes GPS deformation density changes mass redistribution modelling |
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