There are three active volcanoes on the Big Island: Kīlauea, Maunaloa, and Hualālai. Kīlauea has been erupting more or less continually since 1983 from Puʻu Ōʻō vent, and has destroyed close to 200 homes in the Kalapana area. Maunaloa last erupted in 1984, when it sent flows within four miles of the city limits of Hilo. Hualalai's last eruption was in 1801, and the Keahole Airport is built on these flows.
Lava flows always run downhill. At 2000 degrees fahrenheit, lava can destroy or bury everything in its path, including houses, roads and utilities. In addition, volcanoes produce vog, and these sulfuric fumes adversely affect people, especially asthmatics.
On the other hand, volcanoes are one of nature’s most beautiful creations, and the Hawaiian Islands wouldn't be here without successive volcanic eruptions. If you choose to live on the Big Island, you need to learn the basics about volcanoes, as well as mitigation.
Learn what parts of the island are most likely to be impacted by a lava flow and try to avoid these areas when selecting a place to live or build. Also learn where the rift zones are located, what to do if you are asked to evacuate when an eruption threatens, and how to cope with vog.