We have analyzed the creep process in which a vortex loop is disconnecting from a twin boundary or a columnar defect and is then expanding, driven by a transport current. The shape of the vortex loop is in general an arc and not a semicircle. The contact angle α between the loop and the plane of the twin-boundary or the axis of the columnar defect is small if the trapping potential is small. The energy barrier resisting the vortex creep is strongly decreased as α3 for small α. Quantum tunneling through this barrier is analyzed for a massless vortex motion governed by the Magnus force. The tunneling rate W is strongly enhanced for small contact angles with lnW∼α5.