  This article is devoted to the construction of pseudomodes of one-dimensional
biharmonic operators with the complex-valued potentials via the WKB method. As
a by-product, the shape of pseudospectrum near infinity can be described. This
is a newly discovered systematic method that goes beyond the standard
semi-classical setting which is a direct consequence. This approach can cover a
wide class of previously inaccessible potentials, from logarithmic to
superexponential ones.
