Which type of pressure is essential for artesian groundwater to rise above the aquifer?

Hydrostatic pressure is crucial for artesian groundwater to rise above the aquifer because it refers to the pressure exerted by a fluid due to the force of gravity acting on it. In the context of an artesian well, this pressure arises from the confined aquifer, where water is trapped between impermeable layers. When the pressure within the aquifer exceeds the atmospheric pressure above it, it creates a situation where, if a well is drilled into this aquifer, the water naturally rises to the surface or flows out without the need for pumping.

This rise occurs because the hydrostatic pressure in the aquifer forces the groundwater upward, often resulting in a pressure head that can elevate the water far above the aquifer layer itself. Understanding this principle is fundamental in hydrogeology as it explains how groundwater systems can supply water to surface levels without mechanical assistance.