Volcano Watch — The 1955 eruption: spur to a new era of understanding Kīlauea

The 1955 eruption in lower Puna, described in last week's column, was destructive. About 1,580 hectares (3,900 acres) were covered by 108 million cubic meters (141 million cubic yards) of lava, mostly `a`a. Of the covered land, about 450 hectares (1,100 acres) were under cultivation in the Kama`ili, Kehena, Ke`eke`e, Kau`eleau, and Kapoho areas. Approximately 10.1 km (6.3 miles) of public road were buried, as were many kilometers (miles) of cane-field roads.

Iwasaki Camp, in Kama`ili near the upper big bend in the road to `Opihikao, was overrun, but fortunately some of the houses and all personal belongings had been removed. Tragically, surviving remnants of the camp were destroyed on the last day of the eruption, May 26. In all, 21 houses were overrun by `a`a during the eruption.

In March, an earthen barrier 300 m (1,000 feet) long and 3 m (10 feet) high was hurriedly bulldozed in an attempt to save Iwasaki Camp. Twice the flow stopped just after encountering the barrier. But in May, `a`a followed a different route down the steep slope far from the barrier and engulfed the camp.

Other barriers were started on March 22 to protect the Yamada coffee plantation near the coast below Iwasaki Camp. These barriers worked to some degree, certainly delaying `a`a from penetrating the plantation. However, part of the Ke`eke`e flow eventually passed beyond the southwest end of the barriers, and, on March 28, swept across the plantation and into the sea.

The partial success but ultimate inadequacy of these barriers, and of those built during the 1960 Kapoho eruption, fuel a controversy that continues to this day among volcanologists. Feelings run high whenever the feasibility of lava barriers is discussed. This disagreement is apart from the social ramifications of diverting lava from one property to another.

A less controversial discovery during the 1955 eruption was that the summit of Kīlauea responded to what was happening in lower Puna--although only after a delay of about eight days following the start of the eruption. Before 1955, HVO scientists had speculated that sinking of the summit area might accompany migration of magma into the east rift zone. But it was hard to be sure, because the last east-rift eruption occurred in 1923, when monitoring instruments were both sparse and crude.

In 1955, the rift zone actually swelled near the site of the initial outbreak on February 28 near Pu`u Honua`ula. The swelling was detected by the pendulum on a seismograph in Pahoa. Geochemical studies suggest that the swelling was caused by magma rising from an independent reservoir in the area, not by pressure from Kīlauea's summit. The swelling was erased by the eruption; repeat surveys made before (for a new highway southwest of Kapoho) and after the eruption showed sinking and spreading of several tens of centimeters (more than 1 foot) in the eruptive area.

On March 7, Kīlauea's summit began to sink as magma migrated into the east rift zone to replenish that already erupted. This magma mixed with some stored in the rift zone and erupted when the vents shifted uprift of the Pu`u Kali`u area on March 12. Classic geochemical and mineralogic studies of this magma have led to interpretations that enhance understanding of the magma plumbing system at Kīlauea. Unfortunately, the magnitude of subsidence accompanying the migration of magma was uncertain owing to the inadequate instruments of the time.

The 1955 eruption spurred HVO to upgrade its instruments. Opportunities had been missed for characterizing the ground movements. Working feverishly during the next 4 1/2 years, Jerry Eaton and colleagues devised a tiltmeter system and better seismic coverage that were completed just in time for the 1959 summit and 1960 Kapoho eruptions. The new instruments provided data about those two eruptions that form the underpinnings for many of today's ideas about how Hawaiian volcanoes work.

Volcano Activity Update

Eruptive activity of Kīlauea Volcano continued unabated during the past week, and a glow from Pu`u `O`o crater was visible at various times. Lava is erupting from Pu`u `O`o and flowing through a network of tubes toward the coast. One flow is entering the ocean at Lae`apuki, and a second flow, located to the east of the first flow, is active in the area mauka of Waha`ula. An `a`a flow is cascading down Pulama pali from a breakout of this eastern flow. The public is reminded that the ocean-entry areas are extremely hazardous, with explosions accompanying unpredictable collapses of the new land. The active lava flows are hot and have places with very thin crust. The steam clouds are highly acidic and laced with glass particles.

There were no earthquakes reported felt during the week ending on March 2.