Volcano Watch — Lava lakes, islands, and bubbles: 100-year-old descriptions still useful today

With the lake surface at a depth of about 35 m (115 ft) below the crater rim, the team was able to lower an iron kettle into the lake to obtain a lava sample and a thermal probe to measure the lava temperature.

By mid-August, the lava level was receding and soon out of reach for Perret's experimental tools. So, he settled in to observe, photograph, and track the subsidence of the lava lake using measured angles and trigonometry. (Note for students doubting its real-world applications—trigonometry is useful!)

Although Perret had extensive experience with Italian and Caribbean volcanoes, what he observed in Halema‘uma‘u still amazed him: Slabs of solid lava floated and drifted on the lava lake surface, forming "islands" that occasionally broke up and sank, and, at times, rose back up above the surface of the lake.

But one of the most unusual sights he witnessed was the growth and movement of a large gas bubble of volcanic glass attached to a submerged island, which was visible for only five hours. Perret published only two dark photographs of the bubble as it moved across the lava lake, but his written description fills in much of what the photographs fail to show:

"Everything appeared to be normal, however, until 1.30 P. M. of the 18th [of August], when, in a momentary clearing away of the smoke, an extraordinary object was seen, floating far out in the center of the lake. A huge, sausage-shaped, gas-inflated balloon of black lava glass—triangular or box-shaped at one end and cylindrical at the other—was making its way across the lake. A lava fountain, boiling continuously under the eastern end, gave the appearance of a screw propeller, and this most amazing contrivance seemed to be navigating the lake under its own power like a great whaleback steamer, or a black Zeppelin airship. Its length was not less than 170 feet and the cylindrical portion about 30 feet in diameter."

He interpreted the bubble to be the result of a large island breaking up and sinking. As molten lava covered the island fragments, gas was released, which, in turn, inflated a large bubble.

Perrett used the buoyancy of lava lake "islands" to deduce the density of the lava. Interestingly, he came up with ideas quite similar to those that HVO scientists are developing now, 100 years later. For instance, he noticed that the islands did not always rise with rising lava lake levels, and recorded his observation as follows:

"It is true that a steady and continued rise of the lava will float an island upward, but in the case of those comparatively rapid oscillations of level … and especially so during a general subsidence of the lava column, the surface of the lake may rise or fall to the extent of from one to several meters without moving a large island vertically by so much as a single millimeter."

Many of the behaviors exhibited by 1911 and 2011 lava lakes are similar. In particular, the rapid drain-and-fill cycles, when the lava lake level rises over several minutes and then rapidly falls with vigorous bubbling as gas is released, are most likely what Perret described as "rapid oscillations."

Today, HVO scientists are convinced that lava lake oscillations within the current Halema‘uma‘u Crater vent are the result of a lava foam layer periodically building and collapsing on deeper and denser molten lava. The foam is much less dense than typical molten lava, which explains why, in 1911, the islands were not floated by the more rapid variations.

As we approach HVO's Centennial, it is important to continue regular observations of Hawaiian volcanic activity. It's equally important to make use of descriptions, photographs, and data from all previous observations and measurements, like those provided by Perrett.

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Volcano Activity Update

A lava lake has been present within the Halema‘uma‘u Overlook vent over the past week, resulting in night-time glow visible from Jaggar Museum. The lake remains deep within the vent cavity, with minor spattering along the lake margin.

On the east rift zone, a perched lava lake has remained active in the east portion of Pu‘u ‘Ō‘ō Crater over the past week, and an additional vent on the west end started erupting flows onto the crater floor on Monday, August 29. As of Thursday, September 1, lava had filled the crater to within about 25 m (82 ft) of the east rim of Pu‘u ‘Ō‘ō, but was still below its level prior to the August 3 flank breakout and crater collapse.

One earthquake beneath Hawai‘i Island was reported felt this past week. A magnitude-2.8 earthquake occurred at 9:02 a.m., HST, on Wednesday, August 31, 2011, and was located 13 km (8 mi) east of Lō‘ihi Volcano at a depth of 45 km (28 mi).