By monitoring the changes in chemistry and temperature of groundwater, surface water, and steam at a volcano over time, scientists can obtain useful information about changes in volcanic activity. These volcanic hydrothermal systems contain elemental components that signal the presence of magma, such as magmatic carbon dioxide or high helium-isotope ratios (3He/4He). Hydrothermal monitoring sites at Cascades volcanoes include instruments that measure water pressure (to calculate flow rate), temperature (to calculate quantities such as heat flow), and conductivity (to calculate concentrations of elements or chemicals). Scientists visit these sites regularly to take samples of liquid and gas and measure the rate of water flow. The results from these measurements indicate baseline conditions, help researchers determine whether hydrothermal activity is changing, and can indicate the presence or absence of fresh magma.