vertical line in Panel (a) of Figure \[prom\] shows the position of the slit used.

Panel (a) of Figure \[timedist\] shows the time-distance plot, where the bright, rising region is the rising lip of the plume. The cross marks show the top of the plume. This is calculated as the pixel with the greatest intensity change from the pixel below change multiplied by the pixel intensity. Using these pixels, the velocity of the plume and the velocity error were calculated to be $v_{plume}=12.3 \pm 0.6$kms$^{-1}$. As this rise velocity is calculated from a time-distance diagram, it should be viewed as a lower limit on the velocity. The dashed line in the figure shows a velocity of $\sim 12$kms$^{-1}$. Throughout the rise of the plume, the rise velocity can be seen to be approximately constant.

![Panel (a) shows time-distance diagram along the slit shown in Figure \[prom\] panel (b). The cross marks show the position of the top of the plume. The rise velocity of the plume is found to be $\sim 12$kms$^{-1}$. Panel (b) shows the dimensions of the ellipse used to model the rising plume.[]{data-label="timedist"}](figure10_a.eps "fig:"){height="8cm"} ![Panel (a) shows time-distance diagram along the slit shown in Figure \[prom\] panel 