Volcano Watch — November earthquakes

November is a month that always makes HVO seismologist Jennifer Nakata a little nervous. Nakata says her discomfort surfaces about this time each year as she recalls two of the Big Island's most damaging earthquakes, the magnitude-7.2 Kalapana quake that struck on November 29, 1975 and the magnitude 6.6 Ka`oiki quake that shook the island on November 16, 1983.

Nakata had been on the staff for only one year when the Kalapana earthquake, the strongest quake of the century, hit. At 3:36 a.m. a magnitude 5.7 foreshock jolted Nakata and most other Island residents awake. The main event, which was centered 9 kilometers (~6 miles) beneath the Kalapana area, ripped through the island about an hour later.

The intense shaking, which was felt as far away as Maui and Oahu, caused major ground deformation, property damage, and electrical outages throughout the Hilo, Puna, and Ka`u districts.

In Puna and Ka`u, gaping fissures opened, and car-sized boulders tumbled down the steep pali faces and crater walls in Hawaii Volcanoes National Park. The southeastern coastline subsided 3.5 meters (~11 feet) near Halape, generating a local tsunami that washed inland to 14.6 meters (~ 48 feet) above sea level and killed two overnight campers. The quake also triggered a short-lived eruption along a 500 meter-long (~1650 feet) fissure in Kīlauea caldera.

In downtown Hilo, windows shattered and water pipes broke. Septic tanks caved in, houses shifted from their foundations, and merchandise fell from shelves in the stores. Separation cracks opened between walls and floors at the hospital and at several schools and libraries. The Hawai`i Civil Defense Agency estimates that the 1975 Kalapana earthquake caused more than four million dollars in damage.

The Ka`oiki earthquake in 1983 was another early-morning jolt. At 6:13 a.m. a rupture occurred at a depth of 11 km (~7 miles) beneath the Kapapala Forest Reserve located between the flanks of Mauna Loa and Kīlauea Volcanoes. The violent shaking, which was felt for nearly a minute, threw houses from their foundation, downed water tanks, and cut telephone and electric lines across much of the southeastern part of the Island.

Kīlauea's summit was particularly hard hit by the tremblor. Nakata and other HVO staff arriving at the observatory that morning were met with a jumble of toppled scientific instruments, leaking water pipes, and severed utility lines. Large sections of Crater Rim Drive in Hawai`i Volcanoes National Park collapsed into Kīlauea caldera. In Volcano village, houses were moved off their foundations by as much as three feet, and many water tanks and carports collapsed.

Hilo and Kaumana areas were also heavily damaged. Walls and ceilings in homes and businesses cracked. Plate glass windows broke, and rock veneers fell off buildings. Water pipes and utility lines were disrupted, and roadways cracked.

Although of a lesser magnitude than the 1975 Kalapana earthquake, the 1983 Ka`oiki quake resulted in greater economic loss due to increased urbanization of the island. Hawai`i Civil Defense damage estimates top seven million dollars.

Earthquakes are inevitable in this island paradise, but residents can take steps to mitigate their damaging effects. Adhere to the building codes established for the Big Island, secure propane and water tanks, prepare an emergency cache of food and water, and head for high ground if you're at the beach during an earthquake. And, says Nakata jokingly, keep your fingers crossed in November!

Volcano Activity Update

There were no felt earthquakes on the island this week. The current East Rift eruption of Kīlauea Volcano continued without significant change.