The rapid onset of unrest at Mount St. Helens on September 23, 2004 initiated an uninterrupted lava-dome-building eruption that continued until 2008. The initial phase produced rapid growth of a lava dome as magma pushed upward. As shown in the video, an initial succession of lava spines, two recumbent and one steeply sloping, grew to nearly 500 m in length before disintegrating into mounds of rubble. The trajectory of lava extrusion was affected by the geometry of the crater, particularly the proximity of the vent to the south crater wall, and by the growing volume of erupted material.