Here's how it works:

* Aquifer: A layer of rock or sediment that can hold and transmit groundwater.

* Impermeable rock: Rock layers that do not allow water to pass through (like clay or shale).

* Pressure: When the aquifer is trapped between two layers of impermeable rock, the weight of the water above creates pressure.

* Artesian well: If you drill a hole into this pressurized aquifer, the water will rise up the well, sometimes even flowing out at the surface without pumping. This is because the pressure in the aquifer is higher than the atmospheric pressure at the surface.

Let me know if you have any other questions about groundwater!