Volcano studies are carried out among four disciplines: geology, seismology, geophysics and geochemistry. Scientists from each of these disciplines use a variety of techniques and instruments to monitor active volcanoes. For example, geologists map lava flows and assess hazards, seismologists study earthquakes, geophysicists use GPS to track ground movements, and geochemists study gases to characterize magma depth and volume. Together, these techniques comprise a toolkit to better understand a volcano's hazards and activity. USGS Hawaiian Volcano Observatory volcanologist Mike Poland explores the many tools used to monitor active volcanoes, and how applying multiple tools can lead to entirely new insights into how Hawaiian volcanoes work.