The Hawaiian Volcano Observatory (HVO) is an agency of the U.S. Geological Survey (USGS) and one of five volcano observatories operating under the USGS Volcano Hazards Program. Based in Hilo, Hawaii, the observatory monitors six Hawaiian volcanoes: Kīlauea, Mauna Loa, Kamaʻehuakanaloa, Hualālai, Mauna Kea, and Haleakalā, of which, Kīlauea and Mauna Loa are the most active. The observatory has a worldwide reputation as a leader in the study of active volcanism. Due to the relatively non-explosive nature of Kīlauea's volcanic eruptions for many years, scientists have generally been able to study ongoing eruptions in proximity without being in extreme danger.