An FTIR instrument is set up on the rim of Halemaʻumaʻu Crater to measure volcanic gases from the summit lava lake. The open-path Fourier transform infrared (FTIR) spectrometer continuously measures the gases in a volcanic plume, measuring the relative abundance of each. Most of the gas emitted during a volcanic eruption is water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide(SO2). Photo taken Sunday, February 12, 2017 courtesy of USGS/HVO