L y

R y FIGURE 1. Sketch of colliding ux tubes in cross section. The solid lines are the tube boundaries. The radius of the isolated tube is R, the length of the interaction region is L, the y axis is chosen parallel to the contact surface, and is the fractional deformation. 16 y x L V in V in V A V A l 2b FIGURE 2. (a) Sketch of the magnetic ux surfaces of the colliding tubes, projected onto the axial cross section. Reconnection can take place within a thin layer along the contact surface. (b) Sketch of the Parker-Sweet reconnection geometry, which we assert ensues once the connguration shown in Figure (2a) is established by the collision. The y axis is again the contact surface and v in corresponds to the incoming tubes. In slow collisions omly a slight pileup of magnetic ux is suucient to permit Sweet-Parker reconnection.