Radiance maps showing the O IV emissivity of the surges. From left to right: radiance maps in the core of the Mg II k 2796.3 Å line (first column); in the core of the O IV 1401.2 Å line (second column); in the blue and red wings at −50 and 50 km s⁻¹ of O IV 1401.2 Å (third and fourth columns, respectively); and composite image of the blue and red wing radiance maps for O IV 1401.2 Å (fifth column). Equivalent maps are plotted for the O IV 1399.8 Å line (sixth to ninth columns). The contours in all the panels delimit the bulk of the surges visible in the Mg IIk 2796.3 Å radiance maps. The black arrow in the third panel of the first row indicates the location of enhanced O IV emission associated with finger-like threads of a surge. The O IV maps show a horizontal strip of hot pixels that does not affect our findings.