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pure and applied geophysics

, Volume 161, Issue 7, pp 1415–1431 | Cite as

Gravity Changes and Internal Processes: Some Results Obtained from Observations at Three Volcanoes

  • Gerhard JentzschEmail author
  • Adelheid Weise
  • Carlos Rey
  • Carl Gerstenecker
Article

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.

Key words

Gravity changes at volcanoes GPS deformation density changes mass redistribution modelling 

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Copyright information

© Birkhäuser Verlag, Basel, 2004

Authors and Affiliations

  • Gerhard Jentzsch
    • 1
    Email author
  • Adelheid Weise
    • 1
  • Carlos Rey
    • 2
  • Carl Gerstenecker
    • 3
  1. 1.Institut für GeowissenschaftenFriedrich-Schiller Universität, Burgweg 11JenaGermany
  2. 2.INGEOMINAS (Instituto de Investigationes en Geosciencias, Mineria y Quimica)Santafe de BogotaColombia
  3. 3.Institut für Physikalische GeodäsieTechnische Universität Darmstadt, Petersenstr. 13DarmstadtGermany

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