Knowing a volcano's eruptive history is crucial to understanding its potential future behavior and identifying areas most likely to be affected by future activity. Since the inception of HVO, many scientists have worked to make detailed geologic maps of Hawai`i's volcanoes that show areas covered by lava flows of different ages and the locations of faults and various volcanic features, such as cones, fissures, craters, and earlier calderas, the extent of explosive tephra deposits, and even glacial deposits on Mauna Kea.
Such detailed investigations continue today, including studies of numerous tephra layers erupted by Kilauea Volcano in the past 2,000 years and buried beneath younger lava flows. The layer of volcanic ash, pumice and reticulite shown above (brown deposit) was erupted more than 700 years ago, probably from a vent in the upper east rift zone. Deposits such as this form excellent markers than are useful in determining the eruptive history of Kilauea.