Rising magma and groundwater invariably interact. Heating of a confined aquifer will raise porewater pressures, usually over the course of weeks to years. Mechanical strain of a confined aquifer will raise or lower porewater pressures rapidly over minutes or hours. The magnitude of changes in pore pressures can be estimated from assumed or measured changes in temperature and strain. Changes in porewater pressure will be reflected in well-water levels and in spring discharges, and particularly pronounced increases in pore pressure can cause uplift and hydrofracturing. Groundwater will absorb water-soluble gases such as SO₂ and HCI, masking those gases from measurement at the surface. Groundwater that is heated to boiling temperatures can flash and generate banded tremor, some very long-period earthquakes, and phreatic explosions. Some volcanic unrest that has previously been interpreted solely in terms of magma should now be reinterpreted in terms of magma-groundwater interaction.