  Application of a sufficiently strong electric field to an aqueous solution
induces a phenomenon known as `electrohydraulic discharge'. The electric field
causes the water to break down, generating either a corona (at lower field
strengths) or a pulsed arc (at higher field strengths). The discharge typically
results in a complex combination of physical processes (e.g., cavitation and
light emission) and chemical reactions (e.g., generation of free radicals and
nonthermal plasmas). The combination of physical and chemical processes tends
to destroy any organic molecules present, and accordingly electrohydraulic
discharges are currently being investigated as a potentially inexpensive and
environmentally friendly means for purifying drinking water and removing
contaminants from wastewater.
  Two types of electrode configurations have been the main focus of research to
date: (i) a `one-phase' system with both electrodes immersed in water, or (ii)
a `two-phase' system with one electrode in air and the other submerged in
water. In this fluid dynamics video, we demonstrate the striking consequences
of triggering an electrohydraulic discharge in a two-phase system comprised of
water and a viscous, insulating oil. An air/water interface typically remains
stationary until the discharge occurs; in contrast, the oil/water interface
deforms into a conical shape (i.e., a Taylor cone) stretching from the water
phase toward the oil-immersed electrode. The behavior after the cone contacts
the electrode depends sensitively on the properties of the water and oil, and
we demonstrate that, under appropriate conditions, destructive explosions
occur.
