you cant have a Power Aura for Lava Surge. The reason is because it procs a CD reset, but not a buff. Without a Buff power auras has nothing too look for.
what you can do, however, is use Mik Scrolling Battle Text addon, and custom set up an alert to blare in your face when lava surge procs.
---------- Post added 2010-10-13 at 10:58 PM ----------
Ok wait, scratch what i said, you can use Power Auras.
Set up an aura to display on "Action Usable" and whenever Lava Burst is off CD the aura will display. essentually showing whenever lava surge procs.