Volcano Watch: The art and science of geologic mapping

Examples of Hawaii geologic maps. The lefthand map is a USGS Hawaiian Volcano Observatory map created on Sept. 17 within hours of remote sensing (helicopter overflight) of the eruption that occurred from Sept. 15–20. Several age ranges for lava flows of interest are noted by color changes, with those that erupted from 1790–2018 in purple (older lava flows are gray), those erupted on Sept. 15 in pink, and those erupted Sept. 16–17 in red (with the active fissure as a yellow line). The righthand geologic map is that of the Island of Hawaiʻi from the Geologic Map of the State of Hawaii by Sherrod and others (2021). This map was compiled through decades of work and displays the various lava flows, tephra deposits, and other rock and sediment types mapped through fieldwork and remote sensing. The primary purpose of this geologic map is to show all mappable geologic units with their colors denoting their source volcano and age. (USGS/graphic)

Geologic mapping has been one of the most fundamental mandates of the U.S. Geological Survey (USGS) since its establishment in 1879. Congress created the USGS to “classify the public lands and examine the geological structure, mineral resources, and products within and outside the national domain.”