At a deep-sea hydrothermal vent, about how hot can the seawater get while still staying liquid?

The answer

NOAA puts vent fluids above 370 °C (700 °F). Extreme pressure at those depths shoves the boiling point well past that, so the fluid stays liquid until it hits near-freezing seawater and dumps its minerals as black-smoker chimneys.

Correct answer: Over 370 °C (over 700 °F)