Here’s an article I found for you:
“The hottest springs in the deepest part of the lake, at 125 m (410 ft) below the water, have a temperature of 174 °C (345 °F).”
Our hot spring on the ranch has ‘superheated water’ which is water that can have a temp of more than 100C but it doesn’t boil until after it reaches the surface.
You can replicate this effect at home by using a very clean pyrex container and then putting in a couple cups of water with a few tablespoons of baking soda. Heat it for as long as you’d typically need to boil water and then heat it twice that time.
Do not touch it. But put in a thermometer like you’d use for frying donuts and check the temp. It can be as much as 350F at sea level.
Then leave it alone until it cools. It can boil suddenly and explosively. This is not an experiment to do with the kids or without heavy gloves and a thick coat on.
Fair point! I didn’t account for pressure at depth, nor for mineral content.