The overflow of Halema‘uma‘u Crater on February 23, 1918. Photo by T.A. Jaggar from the HVO Record Book courtesy of Bishop Museum.

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

In early 1918, visitors swarmed to Kīlauea Volcano to see a splendid show. The molten lake in Halema‘uma‘u had been rising and the pit was almost full. Soon lava spilled over the crater rim onto the floor of Kīlauea’s summit caldera, destroying part of an automobile road, as well as the visitor viewing area near the rim.

In this week’s featured photograph, Isabel Jaggar, wife of Hawaiian Volcano Observatory Director Thomas A. Jaggar, Jr., stands near the edge of Halema‘uma‘u on the morning of the first overflow. To her left is a wooden A-frame constructed in 1911 to suspend a cable across the crater for taking lava samples and temperature measurements. The next day this old landmark was surrounded by lava and burned. To the right of Mrs. Jaggar, portions of the congealed lava crust have been thrust high above the caldera floor.

With the hot lava so accessible, hundreds of volcano watchers flocked to the area to take photos and meet Pele up close. In the weeks that followed, the overflow destroyed many sites on the caldera floor that tourists had frequented in the past. Volcanic features with fanciful names such as “The Devil’s Picture Frame,” were covered by lava, and this was just the beginning.

Over the next three years, as the magma column at Kīlauea rose and fell the lava lake in Halema‘uma‘u repeatedly overflowed and flooded the caldera floor.

For decades, tourists had singed post cards at hot cracks known as the “Postal Rift.” In April, 1919, lava poured out of the Postal Rift, and by November, this flow had reached the bluff below the Volcano House, burying the trail that led from the hotel to Halema‘uma‘u Crater. By the end of 1919, most of the old volcano landmarks in the summit caldera were gone.

Such overflows of Halema‘uma‘u were common in the past. Since 1868, large infusions of magma had filled the pit and had flooded the caldera floor many times. On each occasion, the lava lake later receded as magma drained away, reopening the home of Pele, only to have the pit gradually refill as the cycle started over.

Sporadic overflows continued until March of 1921, when lava from Halema‘uma‘u and an adjacent cone flowed through a gap in the south caldera and into the Ka‘ū Desert. Since then, Halema‘uma‘u Crater has never overflowed again. While many eruptions have occurred in Kīlauea Caldera since the 1920s, almost a century has passed and Halema‘uma‘u remains only partially refilled.

What caused this change in the behavior of KÄ«lauea? One answer is that Halema‘uma‘u doubled in diameter during the explosive eruption in 1924, so it takes more lava to fill the crater. But, that’s not the most important part of the story.

Changes in the rate of magma supply to the volcano and in the geometry of the plumbing system that carries magma from the summit into the rift zones have kept the floor of Halema‘uma‘u far below the rim. For the crater to fill to overflowing, the magma supply would have to increase and remain high, or conduits to Pu‘u ‘Ō‘ō and other areas on the rift zones of Kīlauea would have to constrict.

In other words, an overflow of Halema‘uma‘u Crater will require a substantial increase in magmatic pressure at the summit of Kīlauea. We see no signs that Pele has such a house cleaning planned any time soon, but if and when she does, it will be a spectacular display.