Where do the gas and hot water from the hot springs come from?

The island of Pantelleria is the emerged part of an imposing submarine volcanic complex whose explosive activity dates back to about 324,000 years ago. Current volcanic activities are limited to hydrothermal and exhalative phenomena, although the last eruption (submarine) occurred in 1891.
Fumaroles and hot springs are common on the island, such as those around Lake Bagno dell'Acqua, with temperatures between 35 and 55°C and bubbling gases mainly consisting of carbon dioxide.
The thermalism and degassing of the springs occur due to the rise of very hot and mineralized fluids, originating from more than a kilometer deep, which rise along large fractures in the Earth's crust, mixing with seawater and the aquifers of volcanic rocks.