It is hot, or at least very warm. But, as you know it cannot be too much higher than the boiling point of water, even if it contains minerals and other chemicals. The reason it's is so blue in the center is that the middle is deeper than the parameters. Parameter is where the water has less motion, therefore it has more time to deposit it's minerals.
"After the first glass, you see things as you wish they were. After the second, you see things as they are not. Finally, you see things as they really are, which is the most horrible thing in the world."
--Oscar Wilde on Absinthe