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| In the years between 1980 and 1991, a large area surrounding Mount St Helens was known to be deforming, resulting in a total of 1-3 cm of uplift. This uplift was measured by trilateration surveys conducted in 1982 and 1991 and was interpreted to be the result of post-eruptive recharge of a deep magma chamber beneath Helens. Interestingly, through the time of the eruption, no further deformation was measured through a synthesis of trilateration data, collected on a broad scale, and campaign GPS surveys conducted in 2000 and 2003, at 17 stations within 5km of the crater. However, if the total displacements from 2000-2003 were small, less than 2 cm, they may have been below the survey’s level of detection. Additional measurements made by a continuous GPS station located at the Johnston Ridge Observatory, approximately 9km away from the crater, did not indicate any surface deformation. | In the years between 1980 and 1991, a large area surrounding Mount St Helens was known to be deforming, resulting in a total of 1-3 cm of uplift. This uplift was measured by trilateration surveys conducted in 1982 and 1991 and was interpreted to be the result of post-eruptive recharge of a deep magma chamber beneath Helens. Interestingly, through the time of the eruption, no further deformation was measured through a synthesis of trilateration data, collected on a broad scale, and campaign GPS surveys conducted in 2000 and 2003, at 17 stations within 5km of the crater. However, if the total displacements from 2000-2003 were small, less than 2 cm, they may have been below the survey’s level of detection. Additional measurements made by a continuous GPS station located at the Johnston Ridge Observatory, approximately 9km away from the crater, did not indicate any surface deformation. | ||
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| Because of the wide spatial and temporal spacing, and to a lesser extent, the levels of noise, in data collected by trilateration and GPS, no conclusions could be made about any potential surface deformation that may have occurred locally on the edifice or within the crater of Helens. The ability to produce spatially continuous maps of surface displacements gives InSAR the ability to resolve the question of whether localized deformation may have occurred at Mt St Helens prior to its 2004 eruption. A study conducted by Poland and Lu in 2008 attempted to image both pre and post eruptive deformation at Mount St Helens using interferogram stacking. Because of decorrelation caused by the presence of snow and dense vegetation, even stacks of interferograms were unable to obtain signal within the crater or on the edifice prior to the eruption (Fig ##). While the results prior to the 2004 eruption were inconclusive, post eruptive results successfully imaged subsidence around and on parts of the edifice. | Because of the wide spatial and temporal spacing, and to a lesser extent, the levels of noise, in data collected by trilateration and GPS, no conclusions could be made about any potential surface deformation that may have occurred locally on the edifice or within the crater of Helens. The ability to produce spatially continuous maps of surface displacements gives InSAR the ability to resolve the question of whether localized deformation may have occurred at Mt St Helens prior to its 2004 eruption. A study conducted by Poland and Lu in 2008 attempted to image both pre and post eruptive deformation at Mount St Helens using interferogram stacking. Because of decorrelation caused by the presence of snow and dense vegetation, even stacks of interferograms were unable to obtain signal within the crater or on the edifice prior to the eruption (Fig ##). While the results prior to the 2004 eruption were inconclusive, post eruptive results successfully imaged subsidence around and on parts of the edifice. | ||
