GPS ground deformation patterns at Mount St. Helens (Washington, USA) from 2004 to 2010

Abstract

GPS measurements on Mount St. Helens spanning the 2004.00-2010.85 time interval, encompassing the 2004-2008 dome-building eruption, were analyzed. First, a local reference frame was derived in order to isolate the volcanic ground deformation from the background tectonic pattern related to the interactions between the Pacific, Juan de Fuca and North American plates. Secondly, the resulting ground deformation patterns were modelled to constrain magmatic sources. Results suggest a vertically elongated magma chamber centred at 8 - 9 km depth beneath the summit area that deflated during the beginning of the dome growth and inflated since January 2008, evidencing that a primary magma reservoir was active both during and after the eruption in a magmatic system persistent over the time.