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March 23, 2000

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


Which way would you drive?

Which way would you drive if you lived on the on the flank of an active volcano with lava headed your way? This question is based on real-life events that happened during the 1950 eruption of Mauna Loa.

On March 25 at 5:43 a.m., a strong earthquake was widely felt across the island.

On May 29 at 3:17 p.m., another strong earthquake shook the island. It was located high on the southwest rift zone. Damage to water tanks and stone walls was reported in Kona. Mauna Loa was building toward its next outbreak.

Volcanic tremor started at 9:04 p.m. on June 1, and a distinct glow appeared to observers at 9:25 p.m.

A 4-km [2.5-mile] fissure opened up, starting at Lua Hou, and proceeded downrift to the 3,840- to 3,350-m [12,600- to 11,000-ft] elevation. The lava from this fissure system headed westward down the mountain. This initial flow moved toward Ho`okena. Which way do you drive?

This flow advanced only 8 km [5 miles] to the 2,740-m [9,000-ft] elevation. A second, more robust flow was moving south-southeast toward Punalu`u. By daybreak on June 2, this flow crossed Kahuku Ranch's mauka road and entered the upper reaches of the Ka`u forest reserve at an elevation of 1,670 m [5,500 ft] after flowing approximately 16 km [10 miles]. Your job is in Hilo, your family in Na'alehu. Which way do you drive?

At 10:15 p.m. on June 1, Hawaiian Volcano Observatory personnel noticed a fume cloud 13 km [8 miles] downrift from the previous vents at the 2,515-m [8,250-ft] elevation. At 10:23 p.m., the illuminated area quickly expanded, indicating that the fissures were actively propagating.

Visual observations indicated two active fissure systems. The upper, extending from the 3,200- to 2,590-m [10,500- to 8,500-ft] elevation, was 9.6 km [6 miles] long. The second, lower, fissure system extended from the 2,500- to 2,380-m [8,200- to 7,800-ft] elevation.

The higher fissure system produced two flows heading westward. The northernmost was called the Honokua flow, the other the Ka`ohe flow. The Honokua flow was fed by fissures between the 2,740- and 3,050-m [9,000- and 10,000-ft] elevation, and lava was moving rapidly. What did this mean for the main traffic corridor surrounding the island? Which way do you drive?

By 12:20 a.m. on June 2, this flow was approximately 1.5 km (1 mile) above Highway 11. By 12:30 a.m., it crossed the highway at the town of Pahoehoe, taking out a gas station, the post office, and several homes. The flow continued toward the ocean and reached it at 1:05 a.m. This flow covered the 24-km [15 mile] distance in less than three hours. By daybreak the activity was greatly diminished, and by noon activity ceased at this locality. Which way do you drive? It was too late for those of you who lived in south Kona-Ka'u; the highway was cut off.

The Ka`ohe flow originated from fissures between the 2,740- and 2,440-m [9,000- and 8,500-ft] elevation. It moved rapidly westward and crossed the highway at 5:00 a.m. approximately 2 km [1.2 miles] south of the Honokua flow near the Magoon ranch. This flow consumed several houses and a coconut grove as it entered the sea around noon on June 2. Twenty-four hours later, observers reported that the Ka`ohe flow had stopped.

From the lower fissure system, a flow called the Ka`apuna lobe originated from the 2,500- to 2,380-m [8,200- to 7,800-ft] elevation late in the evening of June 1. On June 2, at 12:20 p.m., observatory personnel, police, and lava groupies were waiting on highway 11 at the `Ohi`a Lodge, anticipating the arrival of the flow through the forest.

The Ka`apuna flow crossed the highway at 2:00 p.m., 400 m [one-fourth mile] south of the `Ohi`a Lodge and 6.4 km [4 miles] south of the Ka`ohe lobe. By 3:30 p.m., the Ka`apuna flow entered the sea. The flow entered the ocean without explosive activity. A line of steaming water 800 m [one-half mile] from the coast demarked the submarine extent of the flow.

At this point, if you lived south of Yee Hop Ranch, what do you do? Is the eruption over? Which way do you drive?

Late in the evening of June 2 or early June 3, a new lobe originated from the 2,530-m [8,300-ft] elevation. This flow, called the Kahuku flow, moved southward toward Kahuku Ranch. What do you do? Which way do you drive?

On June 8, this flow ceased and reached the 1,920-m [6,300-ft] elevation approximately 9 km [5.8 miles] from the vents.

The Ka`apuna lobe eventually became the focal point of the eruption, and activity waxed and waned until June 23.

Which way do you drive? Everyone should be aware that seismic activity precedes an eruption. When the eruption ensues, and the southwest rift zone of Mauna Loa is the active region, things can happen quickly. It took the Honokua lobe just four hours to cut the highway once the eruption started.

It behooves all of us to listen to the Civil Defense broadcasts for eruption updates. If you live in south Kona-Ka`u and cannot hear the broadcasts, drive to Na`alehu and await CD guidance.

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated during the past week. Lava is erupting from Pu`u `O`o and flowing through a network of tubes toward the coast. Occasional breakouts from the tube system above and on the face of Pulama pali produce short-lived `a`a and pahoehoe lava flows. 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 near Waha`ula and is intermittently entering the ocean. The public is reminded that the ocean-entry areas are extremely hazardous, with explosions accompanying sudden 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 23.

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Updated: 28 Mar 2000