lava is melted rock but below the surface it's called magma the lifeblood of every volcano over many years it collects in a massive chamber miles below the surface here I am in the magma cheber the sound is deafening it's incredibly hot in here close to 1300° the bigger the magma chamber the bigger the eruption some measure 1,000 square miles every once in a while I can get a whiff of the gases because this is where the gases are coming out of the magma magma produces unstable gases which trigger eruptions from this imaginary vantage point the buildup and pressure is easy to see now let's go down deeper and into the mantle where all this magma comes from and where the melting against the Curiosity series Sundays at 9: only on Discovery