The Mechanics of the Explosive Eruption of Kilauea in 1924 
R. H. Finch 1 
Kilauea Volcano staged explosive erup¬ 
tions in May, 1924, after having exhibited 
molten lava almost continuously for more 
than 100 years. The explosions occurred 
during a time of rapid retreat of the lava 
column in Halemaumau (the active vent in 
Kilauea caldera), of a general sinking of the 
mountain top, and of enlargement of Hale¬ 
maumau by engulfment from a diameter of 
1,500 feet to 3,000 feet. Detailed accounts 
of the explosions have been published in 
several journals (Jaggar, 1924: 30-37; Jag- 
gar and Finch, 1924: 353). 
The explosive eruptions in 1924 did not 
establish a precedent for Kilauea, as the sur¬ 
face ash deposits indicate eight or nine quite 
recent explosive periods (Finch, 1924: 1) 
and there are at least two ash beds in the 
walls of Kilauea caldera. The material in 
the surface ash beds indicates that the bulk 
of the ash was produced by a series of mag¬ 
matic explosions (Wentworth, 1938: 101). 
The last explosive eruption of Kilauea prior 
to 1924 was about 1790. Though the ma¬ 
terial thrown out in 1790 was largely acces¬ 
sory, the presence of bombs had led to the 
assumption that all Kilauea explosions were 
magmatic. 
In 1924 the lack of juvenile material was 
not especially conspicuous during the first 
1 Volcanologist, Hawaiian Volcano Observa¬ 
tory, Hawaii National Park. Published by per¬ 
mission of the Director, National Park Service, 
Department of Interior. Manuscript received May 
21, 1947. 
few explosions, since a large part of the 
ejected blocks as well as sand and dust were 
red-hot when they left the Halemaumau rim. 
The large proportion of hot rock was not 
surprising, as shortly before the explosions 
Halemaumau had contained a lava lake 
1.500 feet in diameter and the conduit was 
filled to an unknown depth with hot material 
except for a surface layer of landslide ma¬ 
terial, some of which was hot when it fell. 
In the beginning of the explosive period, 
members of the Observatory wore gas masks 
when making investigations, but it was soon 
found that none of the usual volcanic gases 
was present in an appreciable amount. A 
careful examination failed to find any juven¬ 
ile material in the explosion debris. Some¬ 
what reluctantly, then, we were forced to 
acknowledge that we were dealing with 
phreatic explosions. 
Jaggar (1924: 35) has presented some of 
the evidence pointing to the conclusion that 
the 1924 explosions were due to steam and 
suggested that a talus plug might act as a 
seal in promoting a build-up of pressure. 
The pressure required to produce explosions 
of the magnitude observed was considerable 
—a 14-ton block landed on the Halemau¬ 
mau rim over 1,300 feet above the bottom, 
and an 8-ton one was hurled a distance of 
3.500 feet. The depth from which these 
blocks came and the duration of their accele¬ 
ration (length of the "gun barrel”) is not 
known. The pressure required to make an 
appreciable showing in the bottom of Hale- 
237 
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