GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 56-4
Presentation Time: 2:20 PM


SWANSON, Donald A.1, WANLESS, V. Dorsey2, GADDIS, Ben1 and STOPPA, Line3, (1)Hawaiian Volcano Observarory, U.S. Geological Survey, PO Box 51, Hawaii National Park, HI 96818, (2)Department of Geosciences, Boise State University, 1910 University Drive, Boise, ID 83725-1535, (3)Department of Geosciences, University of Fribourg, Chemin du Musee 6, Fribourg, 1700, Switzerland,

More than 50 phreatic explosions took place at Halemaumau Crater in Kīlauea Caldera during May 10–27, 1924. One person was killed, and at least 7 others suffered minor injuries. We mapped the explosive deposits and reviewed contemporary accounts and photos to anticipate what a similar future eruption might produce.

A ballistic field extends 1.2 km N-S and 1 km E-W from the center of the crater. Measurements of 2200 blocks >25 cm in diameter define a pattern of decreasing size away from the crater. The two largest blocks, weighing ~10 tons, fell near the rim but were engulfed when the crater later widened. A few large blocks with favorable ejection angles and velocities travelled farther than predicted by the overall pattern. For example, one block weighing ~8 tons landed 800 m southeast of the crater. All but one of the 9 measured blocks with average diameter of 1.5–2 m fell southeast of the crater, perhaps ejected from an inclined conduit.

Eruption columns a few kilometers high accompanied the ballistic showers. Their lapilli and ash deposits are now hard to recognize outside the caldera owing to erosion and to the similarity of the 1924 debris to underlying ejecta erupted between 1790 and ~1820. A pumice deposit erupted ca. 1820 forms a datum west of the caldera; lithic lapilli overlying it are likely of 1924 age. A map of maximum clast size shows an asymmetric distribution of lapilli; the 1-cm isopleth is 3 km west of the crater, 2 km east, and 1 km north. The southern extent is uncertain, because the key pumice deposit is absent in this area.

Ash distribution is even more uncertain owing to poor preservation. The 5-cm isopach reaches 2 km north and east of the vent but barely 1 km west and southwest, despite prevalent NE wind during the eruption. We attribute this to water and mainly wind erosion, mostly in the 2-3 decades after 1924. Workers in the 1940s noted that the 1924 ash deposits were already limited to small patches in the windswept area southwest of the crater.

The 1924 eruption was tiny compared to many during the dominantly explosive period between ca. 1500 and the early 1800s. Yet a repeat would pose severe hazards in the area, visited by ~5000 people daily. The eruption punctuated an otherwise effusive period starting ca. 1820, a sobering reminder that Kīlauea can be a dangerously explosive volcano even when it is mostly erupting lava flows.

  • 2016 GSA.pptx (22.1 MB)