User blog comment:Warwolf 51/The Roleplay Random War Room/@comment-7178845-20140206021135/@comment-5889313-20140206133151

Well it would be very high if it wasn't filled with Magma (lava is when it comes out of a volcano), and yes, the pressure change would be radical, and yes, they would pop like a balloon because the pressure in the surface is less than in the Earth's core.