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Volcano Watch — What are our island's worst-case eruption scenarios (part 2)?

December 1, 2005

What might a future eruption in a residential neighborhood be like? We can get our best answer by examining past eruptions in the area such as the 1887 and 1907 eruptions of Mauna Loa.

Illustration of Hawaii's hazard zones
The island of Hawaii is divided into zones according to the degree of hazard from lava flows. Zone 1 is the area of the greatest hazard, Zone 9 of the least.

The 1887 eruption was preceded by an increasing number of felt earthquakes starting in early December 1886. A brief summit eruption lasting a couple of hours was noticed at 8:00 pm on January 16. The rift zone eruption started at about 7:00 pm on January 18 at a location about 4.7 km (3 miles) above what is now Hawaiʻian Ocean View Estates (HOVE). Within 11 hours, the flow had crossed the government road (just below Hawai`i Belt Road). In less than 17 hours, the flow had reached the ocean.

The 1907 eruption was preceded by a "short period of moderate tremors." The eruption started at the summit just after midnight on the morning of January 10, lasted about 3 hours, and then broke out on the southwest rift zone about 4:00 am. The first lava flow crossed the government road early on the morning of January 13. The flow split into two arms, and neither reached the ocean.

As stated last week, the next eruption will most likely start in the summit. Based on the 1887 and 1907 eruptions, the eruption could produce lava flows that would traverse the length of HOVE and cross the Hawai`i Belt Road fewer than 3 days after the start of the summit phase. Any effort to minimize damage and threat to residents of HOVE and Hawaiʻian Rancho Estates would need to be done in fewer than 3 days.

When the next eruption of Mauna Loa starts, civil authorities will be faced with a tough decision. They will know there is a less-than-10-percent chance that the eruption could produce flows that will directly affect HOVE; they also will know that they have limited time to complete evacuation of the 2,000-plus residents of that and nearby subdivisions. Any delay to see whether the eruption will migrate south will cost valuable evacuation time.

There are also residential neighborhoods within Lava Flow Hazard Zone 1 in the lower east rift zone of Kīlauea volcano. All of Leilani Estates, Lanipuna Gardens, and parts of Vacationland Hawaiʻi and Nanawale Estates are within Zone 1.

An eruption in 1840 might be used as an example in this part of Kīlauea. That eruption started on May 30 near the summit. A vent opened north of Leilani Estates and produced a lava flow which entered the ocean five days later. Leilani Estates would have missed that lava flows but not the gas emitted from the vent. Nanawale Estates would have been completely inundated. In addition, the flow would have crossed and blocked all roads out of lower Puna.

What can be done? Those at risk must be prepared to evacuate, and have the means and a plan in place, when directed to do so by Hawai`i County Civil Defense. Those New Orleaneans who were able to evacuate suffered the least disruption to their lives, whereas those who couldn't evacuate, or chose not to, suffered far greater risks, discomfort, and disruption. With as little warning as may be available to communities located on or near lava flow hazard zone 1, it is essential that the residents of these areas develop a personal preparedness plan that includes evacuation from their homes on very short notice.

The community might also wish to identify those in the community who may need assistance and help them make appropriate plans evacuation should a lava flow threaten their community. For additional preparedness information, go to the Natural Hazards web site maintained by the UH-Hilo Center for the Study of Active Volcanoes at: http://www.uhh.Hawaiʻ and the USGS website

Enough doom-and-gloom. HVO will be doing everything it can to provide as much warning as is prudent as the National Weather Service did with Hurricane Katrina. As we can see on the Gulf coast crisis, minimizing the effects of any natural disaster requires constant preparedness of the warning agency (HVO in our volcano's case), the local emergency management agency (Hawai`i County Civil Defense, National Park Service), and residents who choose to live in high hazard areas.

Volcano Activity Update

During the past week, the number of earthquakes located beneath Kīlauea remains at levels typical of the current eruption. Inflation continues at slightly increased rates.

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone. Lava continues to flow through the PKK lava tube from its source on the flank of Pu`u `O`o to the ocean, with a few surface flows breaking out of the tube. In the past week, flows were active on the steep slopes of Pulama pali, above the coastal plain. Surface flows on the pali are visible at night (weather permitting) from the end of Chain of Craters Road.

As of December 1, lava is entering the ocean at East Lae`apuki, in Hawai`i Volcanoes National Park. The large lava delta that had formed at East Lae`apuki collapsed into the ocean on November 28. The size of the delta was about 34 acres. In addition to the delta, about 10 acres of the older adjoining terrain also collapsed. The sea cliff retreated 50 meters (yards) at the point where lava discharges into the ocean. This constitutes the largest ocean-entry collapse during the Pu`u `O`o eruption, which began in January, 1983. The stepwise collapse began at 11:10 and continued until 15:35. These collapse events triggered steam explosions as hot rock and lava mixed with sea water. Rocks and spatter were hurled as much as 100 meters (yards) inland of the new sea cliff. A blanket of smaller particles extended even farther. The collapse truncated the lava tube that had been feeding the ocean entry, and lava shot from the exposed tube several meters below the top of the new sea cliff into the sea, like water from a fire hose. A ramp has now formed beneath the lava stream, and an incipient lava delta has formed at the base of the sea cliff; it is growing rapidly.

Collapses occur without warning and obviously constitute a severe hazard. For this reason, access to the ocean entry and the surrounding area remains closed, though other parts of the flow field are open. If you wish to 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.

There was one felt earthquake reported on Hawai`i Island within the past week. A magnitude-4.5 earthquake occurred at 10:26 a.m. on Tuesday, November 29 and was located 7 km (4 miles) south of the Pu`u `O`o crater at a depth of 10 km (6 miles); it was felt island-wide. November 29 was also the 30th anniversary of the magnitude-7.2 Kalapana earthquake and tsunami that killed 2 and caused well over a million dollars in damage.

Mauna Loa is not erupting. During the past week, the count of earthquakes located beneath the volcano remains at low levels. Inflation continues but has slowed over the past several weeks.

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