By Hawaiian Volcano Observatory Special to West Hawaii Today | Sunday, October 31, 2021, 12:05 a.m.
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Annotated image showing how lava fountain heights are measured using a trigonometric equation. Geologists measure two angles, from eye-level to the top and bottom of the lava fountain. These angles, and the distance between the geologist and the fountain, are used in a trigonometric equation to determine heights of the top and bottom portions of the fountain. The two values are added together to get the total lava fountain height. USGS photo of fissure 22 taken during the 2018 Kilauea lower East Rift Zone eruption on May 20, 2018. (USGS photo by L. DeSmither/Special to West Hawaii Today)
One of the things that field geologists do first is to measure the height of lava fountains and other vent dimensions to help assess how energetic the eruption is. By knowing the height of a lava fountain and measuring its change overtime, geologists can assess short-term and long-term eruption dynamics even if it is not obviously visible hour to hour or day to day.