Most hot springs that are just a little warmer than mean annual temperature (6°- 9°C) acquire their heat .
A) because most of the groundwater is millions of years old from when the Earth's climate was warmer
B) because there are young intrusions everywhere at depth, always warming up the crust
C) by deep circulation through progressively warmer rocks at depth (~2°C per 100 m)
D) because most of the recharge from rainfall is in the warmer summer months

Question

Quizplus · Accepted Answer

Hot springs that are slightly warmer than the mean annual temperature typically acquire their heat through deep circulation of water through progressively warmer rocks at depth. This process is known as the geothermal gradient, where temperature increases with depth at an average rate of about 2°C per 100 meters.

Most Hot Springs That Are Just a Little Warmer Than