Sketch of the emergence process of an anchored flux tube. Proceeding from the bottom panel upwards, a flux tube rises from some anchoring depth, z_a, towards the surface. Phase 1 begins about τ = −1 days when the opposite polarities become visible at the surface with an increasing separation speed (acceleration). We attribute this to the shape of the rising flux tube. Phase 2 begins when the separation speed starts decreasing (deceleration) and ends when the polarities have stopped separating and lie above the subsurface anchored foot-points. We attribute this to a combination of the magnetic tension force acting to straighten the magnetic field after it has expanded above the surface causing the polarities to separate, and the opposing drag force acting on the moving polarities.