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Kilauea Volcano’s 1924 Explosive Eruption Resembles a Crime Scene Investigation

April 19, 2013

Map showing ballistic blocks of the 1924 eruption: red, more than 1.5 m in average diameter; yellow, 1–1.5 m. Shading shows lava flows younger than 1924 outside Halemaʻumaʻu, and dashed line, the limit of ballistic blocks erupted on March 19, 2008. Crater in 1912 widened to nearly its present diameter during the 1924 eruption. (USGS)

The following is this week’s edition of “Volcano Watch” from the Hawaiian Volcano Observatory (USGS).

Sometimes a geologic study resembles a crime scene investigation (CSI), as seen on TV. You piece together information from eyewitnesses and compare it with your own detailed observations to arrive at an interpretation of what happened. Along the way, this may lead to dead ends, resolve many or all uncertainties, or perhaps open new possibilities unexpected when the investigation started.

Explosion column at 0935 on May 13, 1924. Photo by Oliver Emerson, taken from near Kilauea Military Camp. (USGS)

We are interested in learning as much as we can about the explosive events that rocked the summit of Kīlauea for 18 days in May 1924. Why? Because the past is a guide to the future, not infallible, but far better than nothing. The more we know about those explosive events, the better we can estimate the causes and effects of the next explosive pulse at Kīlauea.

The accompanying map shows the distribution of blocks more than 1 m (3.3 ft) in average diameter, hurled out of Halemaʻumaʻu ballistically in 1924, and preserved today. As physicists know, a purely ballistic trajectory is possible only in a vacuum, but we can overlook that nicety for our purposes. Such a map was not prepared in 1924; that is unfortunate, because since then, lava flows have covered parts of the block field. Nonetheless, the distribution of the large blocks observed today shows two striking patterns, one of which was noted by HVO researchers in 1924.

The first is the absence of large blocks on the southwest side of Halemaʻumaʻu. This was noted by Oliver Emerson and Thomas Jaggar in late May and early June 1924. The second, unnoted in HVO records of the eruption, is the concentration of large blocks on the southeastern side of Halemaʻumaʻu, with one eight-ton block strewn as far as 1 km (0.6 mi) from the center of the crater. The largest explosive event in 1924, on May 18, ejected blocks toward the southeast, including the eight-ton block, and killed Truman Taylor.

Otherwise, the distribution of large blocks—and even of smaller ones down to 25 cm (9.8 inches) in average diameter, the smallest we’ve mapped—is reasonably uniform around the crater. In terms of sheer numbers of blocks more than 25 cm across, the northern flank of Halemaʻumaʻu wins, though this can’t be seen on the map of only larger blocks.

These patterns may tell us something unexpected. The maximum concentration of large blocks is near where the Overlook vent opened on March 19, 2008. Is there a long-lasting weak spot in this area?

WHAT CAUSES EXPLOSIVE ERUPTIONS AT KILAUEA? (USGS)

The abundance of large blocks along the northern and eastern rim is consistent with eyewitness reports. Emerson noted on May 28, 1924, that the northeastern part of Halemaʻumaʻu was “vastly deeper” than the southwestern part, which ejected few large blocks. The day before, Ruy Finch commented that “The steam was rising from the usual vent at NE side” of Halemaʻumaʻu. Perhaps there is something long-lasting about this weakness, too. Seismologists today place a magma conduit only a few hundred meters below the northeastern part of Halemaʻumaʻu, and four eruptions have come from this area since 1924.

Many eyewitness accounts conflict with what we see today regarding the material that fell far beyond the ballistic limit south and west of the caldera. Almost all the accounts speak only of ash, yet today we find scattered rocks called lapilli (2–64 mm [0.08–2.5 inches] in diameter) in that area, capping ash that, by definition both then and now, is less than 2 mm (0.08 in) in diameter.

We think that this is a slip-up by the 1924 observers, a confusing shorthand for any particle smaller than a few centimeters across. Such a generalization was often made in the early 20th century, although some written accounts in 1924 actually do mention and even measure fragments a few centimeters in diameter, which they should have termed lapilli or gravel. Unfortunately, it is vital for estimating the energy of the eruptions to know how far these larger stones were dispersed from the vent. Our mapping of this aspect of the 1924 events is in its closing stages, and we will report on the distribution of lapilli and ash in a future Volcano Watch.

For more information on Kilauea Volcano’s continuing eruption, visit the official website of the Hawaiian Volcano Observatory.

This panorama is the latest composite of three images from a temporary research camera positioned in the observation tower at the Hawaiian Volcano Observatory. The camera is looking SSE towards the vent, 1.9 km (1.2 miles) the webcam. For scale, Halemaʻumaʻu crater is approximately 100 m (330 ft) deep. (USGS)

3 Comments leave one →
  1. Hawaii Big Island Travel Guru permalink
    April 19, 2013 2:20 pm

    Thank you USGS Scientists for absolutely fascinating insight into the 1924 Kilauea Summit eruption ~ I loved learning about it, your great visuals and how you cleverly related it to a crime scene! Much Aloha!

  2. szekelyse50 permalink
    April 30, 2013 3:49 am

    Köszönöm ,mindig van egy egy érdekes felfedezés.

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