The Hawaiian Volcano Observatory (HVO) is a volcano observatory located at Uwekahuna Bluff on the rim of Kīlauea Caldera on the Island of Hawaiʻi. The observatory monitors four active Hawaiian volcanoes: Kīlauea, Mauna Loa, Hualālai, and Haleakalā. Because Kīlauea and Mauna Loa are significantly more active than Hualālai and Haleakalā, much of the observatory's research is concentrated on the former two mountains. The observatory has a worldwide reputation as a leader in the study of active volcanism. Due to the relatively non-explosive nature of Hawaiian volcanic eruptions, scientists can study on-going eruptions in proximity without being in extreme danger. Located at the main site is the public Thomas A.