  We analyse the thermally activated depinning of an elastic string (line
tension $\epsilon$) governed by Hall dynamics from a columnar defect modelled
as a cylindrical potential well of depth $V_{0}$ for the case of a small
external force $F.$ An effective 1D field Hamiltonian is derived in order to
describe the 2D string motion. At high temperatures the decay rate is
proportional to $F^{{5}/{2}}T^{-{1}/{2}} \exp{\left
[{F_{0}}/{F}-{U(F)}/{T}\right ]},$ with $F_{0}$ a constant of order of the
critical force and $U(F) \sim{\left ({\epsilon V_{0}})}^{{1}/{2}}{V_{0}/{F}}$
the activation energy. The results are applied to vortices pinned by columnar
defects in superclean superconductors.
