# Critical field observation at Kīlauea in 1915 is finally confirmed in 2007

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Several Volcano Watch articles during the past few years described Kīlauea's explosive eruptions, their surprising frequency, and the large size of some of them. These ideas are not entirely new, however. Writing in 1909, C.H. Hitchcock concluded that Kīlauea "has not always been the tame creature of today."

The Keamoku is the flow crossed by Highway 11 near the park boundary in Kau. It was erupted from Mauna Loa long before 1790.

(Public domain.)

Early research on Kīlauea's explosions focused on when they had taken place. One crucial field observation in this regard was made in 1915, but later workers, unable to duplicate it, assumed it was wrong. This contributed to an incorrect age assignment for some of the deposits encircling Kīlauea's caldera. The original observation was reconfirmed only this year. Here's the story.

Sidney Powers, a 25-year old geologist armed with a fresh Harvard Ph.D. and a coveted traveling fellowship, visited Hawaii for a few short weeks in 1915. Powers, a graduate of Williams College, was a star in graduate schools at MIT and Harvard and probably caught the attention of Thomas Jaggar, founder of HVO in 1912 and a former MIT professor. Whatever attracted Powers to Hawaii, he made the most of his few weeks, gathering enough information to publish 9 papers between 1916 and 1920.

Among his discoveries, Powers observed that the lower part of the Keanakakoi tephra—the name that geologists use for the explosion deposits at Kīlauea's summit—lies directly beneath the Keamoku aa flow. The Keamoku is the flow crossed by Highway 11 near the park boundary in Kau. It was erupted from Mauna Loa long before 1790. Therefore, the explosive deposits under the flow are also older than 1790.

What a find! This was unassailable evidence that some of the Keanakakoi explosions occurred long before the 1790 eruption. Powers' contemporaries were pleased, because they believed without much evidence that only the top of the Keanakakoi deposits was of 1790 vintage. Powers found the proof of this concept, and one would have thought that was the end of the story.

Unfortunately, however, Powers failed to give a precise location for his critical—and probably hard-won—observation, and this led to frustration and ultimate rejection of his observation by later workers. The base of the aa flow is no longer exposed, if it ever was, so it is no easy task to find what is just underneath the flow.

Geologists in the late 20th century identified no place where they could look under the flow. They found some volcanic ash on top of the aa flow, as had Powers, but no pieces of reticulite, the very frothy pumice familiar to many Volcano residents as the crunchy stuff at the base of their soil. Powers had found reticulite under the flow, and its absence on the flow surface was entirely consistent with his observation.

But, imagine Styrofoam packing pellets falling onto a rough aa surface. After a few years, they would almost all be gone, washed and blown into spaces between the rubble. So, the absence of reticulite on the flow surface might simply indicate poor preservation rather than burial by the flow. Late 20th-century researchers adopted this interpretation, considering all of the Keanakakoi, including the reticulite, to be younger than the Keamoku and to have formed in 1790.

What a turnaround from Powers conclusion! The disagreement was glaring and had to be resolved, but the poorly exposed base of the flow bedeviled attempts to check Powers observation. Finally, in a last-ditch effort in January 2007, a place was found near Kipuka Puaulu that almost revealed the flow base. A little scraping uncovered treasure; the bottom of the flow rests on several centimeters of volcanic ash, including the reticulite. Sidney Powers was right after all! The lower part of the Keanakakoi is indeed older than the Keamoku, which radiocarbon ages indicate was erupted 400-500 years ago. The lower part of the Keanakakoi has to be that age or a little older.

Hats off to Sidney Powers! His observational skills at Kīlauea foretold a luminous career. He quickly became one of the leading petroleum geologists of the 1920s before his untimely death in 1932 at age 42. Powers was so respected by his peers that the most prestigious award given today by the American Association of Petroleum Geologists is named in his honor.

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### Volcano Activity Update

This past week, activity levels at the summit of Kīlauea Volcano have been slightly elevated above background levels. The summit caldera has been expanding, indicating inflation, since the beginning of 2007. The number of earthquakes located in the summit area increased from typical levels of less than 10 per day to nearly 20 per day. The earthquakes were concentrated in the upper southwest and east rift zones.

Eruptive activity at Puu Oo continues. The level of activity, while somewhat subdued for several months, has picked up over the last few weeks. On clear nights, glow is visible from vents within the eastern half of the crater, with occasional bright bursts from the easternmost vent. Lava continues to flow through the PKK lava tube at least to where the Campout tube branches off about 1 km south of Puu Oo. The PKK tube may still be feeding small breakouts above the top of the pali, but most, if not all, of the flow is going into the Campout tube.

The frequent streams of lava seen on Pulama pali in early May have died down, and very little incandescence has been seen on the pali for the past week. Breakouts abound, however, on the coastal plain, mostly from the easternmost branch of the Campout tube that has been feeding flows near the base of the Royal Gardens subdivision. These breakouts have been creeping toward the ocean for several weeks and finally reached it on May 16. This new ocean entry?the Poupou entry?is located near the long-buried archeological site of Poupou-Kauka West. It is located within Hawaii Volcanoes National Park about a mile east of the other active ocean entry at Kamokuna. The Kamokuna entry remains small, suggesting that little lava is entering the water. A few small breakouts have also been active about a half-mile inland from Kamokuna.

A portion of the East Laeapuki delta, which last saw active lava in mid-March, collapsed on May 10. After an aerial reconnaissance, the size of the collapse has been upgraded from 16 acres to 23 acres. Fist-sized rocks were blasted up to 460 feet inland but fell within the National Park closure area. Large cracks cut the remaining portions of the delta, and the area remains extremely hazardous.

Access to the sea cliff at East Laeapuki and the active ocean entries is closed, due to significant hazards. The surrounding area, however, is open. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-2.8 earthquake occurred at 7:44 p.m. H.s.t. on Friday, May 11, and was located 5 km (3 miles) south of Volcano at a depth of 3 km (2 miles).

Mauna Loa is not erupting. No earthquakes were located beneath the summit. Extension of distances between locations spanning the summit, indicating inflation, continues at steady, slow rates.