Most eruptions originate at the summits and rift zones of Hualālai, Maunaloa , and Kīlauea. Rift zones are areas where the volcano is rifting or splitting apart. The rock in a rift zone has many cracks and is relatively weak, and thus it is easiest for magma to make its way to the surface through these rift zones. Once at the surface, the lava flows downhill, following local topography. Like water, lava seeks the path of least resistance. Areas downhill of rift zones are more likely to be covered by future lava flows than areas on extinct volcanoes. The U.S. Geological Survey provides lava flow hazard maps.
If you are planning to buy land on the Big Island, first make sure you understand where it is in relation to the rift zones. Visit the Hawaiian Volcano Observatory's Lava Flow Hazard Zones website.