November 28, 1997

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Lava diversion in Hawai`i?

November has been a busy month historically for eruptions as well as earthquakes. Six historical eruptions have started in November on Kilauea (1930, 1959, 1967, 1973, 1975, 1979) and four on Mauna Loa (1880, 1892, 1914, and 1935).

Today's column focuses on the Mauna Loa eruption that began on November 21, 1935. This eruption is notable for several reasons. It began from vents within the rift zone, but, as the eruption progressed, the vents deviated from the rift zone and formed a radial vent on Mauna Loa's north flank.

The 1935 lavas can be easily identified as the black flow surrounding Pu`u Huluhulu on the Saddle Road opposite the Mauna Kea access road. This eruption also marks the first attempt at altering the course of a Hawaiian eruption, through the use of explosives.

The eruption came as no surprise to those working at the Hawaiian Volcano Observatory. It was preceded by two flurries of earthquakes, two months, and, one month prior to the outburst of lava. Each flurry tracked the upward migration of lava within the volcano. The largest recorded earthquake occurred early in the morning of the 21st and was felt on Oahu. The eruption began at 6:20 PM.

Like most Hawaiian eruptions, the eruptive activity was immediately preceded by a swarm of earthquakes, followed by tremor. The eruption commenced with a curtain of fountains near North Pit within the summit caldera, Moku`aweoweo. The vents migrated 3 km (2 miles) down the northeast rift zone.

Here a series of discontinuous fissures began erupting; lava was thrown 60-90 m (200-300 ft) into the air, and flows advanced toward Mauna Kea. These early flows were `a`a because of the vigorous activity at the vent.

In the meantime, the summit activity waned, eventually dying off on November 26. The rift activity finally condensed to a single central vent at the 3,500 m (11,400 ft) elevation.

On November 27, low-level fountaining was reported from the radial vent at the 2,600 m (8,600 ft) elevation on Mauna Loa's north flank (well outside the limits of the rift zone). The initial flows produced from this radial vent were `a`a. By December 8, the vent began producing pahoehoe. On December 22 the pahoehoe flows reached the low area between Mauna Loa and Mauna Kea, ponding near Pu`u Huluhulu and the present day Saddle Road.

Eventually the lava turned to follow the natural drainage toward Hilo, instigating a crisis. On December 26, the flow was moving 1.6 km per day (1 mile per day), and at that rate scientists calculated the flows would reach Kaumana Road by January 9 (disrupting mochi-pounding parties). A suggestion to bomb the eruption was made. The U.S. Army Officer who planned the bombing operation was then Lt. Colonel George S. Patton, who would go on to WWII fame.

On December 27, U.S. Army planes dropped bombs, targeting the lava channels and tubes just below the vents at 2,600 m (8,600 ft). The object was to divert the flow near its source. The results of the bombing was declared a success by Thomas A. Jaggar, Director of the Hawaiian Volcano Observatory.

Jagger wrote that "the violent release of lava, of gas and of hydrostatic pressures at the source robbed the lower flow of its substance, and of its heat." The lava stopped flowing on January 2, 1936. The efficacy of this lava bombing is disputed by some volcanologists, and lava diversion will be the subject of a future Volcano Watch.

Earthquake and Eruption Update, 28 November

The constant effusion of lava from the Pu`u `O`o vent on Kilauea's east rift zone continued unabated during the past week. Confined in a network of tubes, the lava flows from the vent to the seashore and enters the ocean at Waha`ula and Kamokuna benches, at the eastern edge of Hawai`i Volcanoes National Park. Conditions at the coastal entries are very unstable with frequent collapses resulting in explosive activity. Lava viewers are reminded that the area is extremely hazardous.

There were no earthquakes reported felt during the past week.