We present preliminary results on the investigation of one polar crown prominence that erupted on 2012 March 11. This prominence is viewed at the east limb by SDO/AIA and displays a simple vertical-thread structure. A bright U-shape (double horn-like) structure is observed surrounding the upper portion of the prominence before the eruption and becomes more prominent during the eruption. When viewed on the disk, STEREO_B shows that this prominence is composed of series of vertical threads and displays a loop-like structure during the eruption. We focus on the magnetic support of the prominence by studying the structure and dynamics before and during the eruption using observations from SDO and STEREO. We will also present preliminary DEM analysis of the cavity surrounding the prominence.
