The sun can reach 27 million degrees Fahrenheit which is 15 million degrees Celsius. The Japanese like 90+ % of the world use Celsius for their temperature measurements. America primarily still uses Fahrenheit. And magma can't stand up to that whether it were Celsius or Fahrenheit. As Haschwald stated it wasn't even fire at that point as fire can't reach that heat nor can magma. It would actually be plasma in the real world which looks a lot like fire.