The hazard boundaries are approximate, and the change in the degree of hazard is generally gradual rather than abrupt. Finally, any hazard assessment is based on the assumption that future eruptions will be similar to those in the past.
The hazard zones also take into account the larger topographic features of the volcanoes that will affect the distribution of lava flows. Our knowledge of prehistoric eruptions is based on geologic mapping and dating of the old flows of each volcano. Hazard zones from lava flows are based chiefly on the location and frequency of both historic and prehistoric eruptions. 'Historic eruptions' include those for which there are written records, beginning in the early 1800s, and those that are known from the oral traditions of the Hawaiians. The latest map divides the island into 9 zones, with lava flows most likely to occur in Zone 1 and least likely in Zone 9.
The first USGS map showing volcanic hazard zones on the Island of Hawai‘i was prepared in 1974 and revised in 19. Lava-flow hazard zones map, Island of Hawai‘i.
