450 C is over 800 F
http://www.bbc.co.uk/news/science-environment-16493787
The world's deepest known volcanic vents are also the hottest, a UK-led expedition has indicated.
The seafloor vents are located 5km below the surface of the Caribbean, in the Cayman Trough.
The researchers say the structures are shooting jets of mineral-rich water more than a kilometre into the ocean above.
The vents' features suggest the water is warmer than 450C - hot enough to melt lead.
http://www.bbc.co.uk/news/science-environment-16493787