  In this paper, we investigate the scattering of surface waves on reactive
impedance boundaries when the surface impedance undergoes a sudden change in
time. We report three exotic wave phenomena. First, it is shown that by
switching the value of the surface capacitance of the boundary, the velocity of
surface waves can be fully controlled, and the power of reflected and
transmitted surface waves are amplified. Second, we show that when a capacitive
boundary is switched to an inductive one, the surface wave stops completely,
with a "frozen" static magnetic field distribution. The static magnetic fields
are "melt" and restore propagating surface waves when the boundary is switched
back to a capacitive one. Third, we show that temporal jumps of the boundary
impedance couple free-space propagating waves to the surface wave, which is an
analog to a spatial prism. These interesting effects enabled by temporal jumps
of metasurface properties open up new possibilities for the generation and
control of surface waves.
