December 28, 2000

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

A millennium of eruptions in Hawai`i

By anyone's reckoning, New Year's Day either starts a new millennium or ends its first year. What have Hawai`i's four active island volcanoes done during the past 1,000 years?

Let's start with the 20th century. An eruption was going on about 49.6 percent of the time, 48.3 percent at Kilauea and 1.3 percent at Mauna Loa. The two erupted together about 0.3 percent of the time.

At Kilauea, Halema`uma`u erupted for about 9,060 days, Pu`u `O`o and Kupaianaha about 6,575, Mauna Ulu about 1,775, and other sites about 486 days, 253 during ongoing Halema`uma`u activity. Mauna Loa erupted on 599 days, 122 of them in concert with Kilauea. Kilauea spilled out about 2.9 cubic kilometers (3.8 billion cubic yards) of lava and Mauna Loa, about 1.9 cubic kilometers (2.5 billion cubic yards). That's 380 million 10-yard dump-truck loads from Kilauea and 250 million from Mauna Loa.

These figures clearly show that most eruptions of Mauna Loa are much larger than those of Kilauea. Mauna Loa produced about 65 percent as much lava as did Kilauea while erupting only about 3 percent as often.

Lava from several eruptions in the past century both covered land and destroyed buildings, roads, and other structures. Among them, the 1955 and 1960 eruptions in lower Puna, and the Pu`u `O`o-Kupaianaha eruption from 1986 to 1991, were the most damaging at Kilauea. The 1926 and 1950 eruptions of Mauna Loa were also very destructive.

Two Kilauea eruptions led directly to fatalities, one from an explosion at Halema`uma`u in 1924 and three at the coast during the ongoing eruption.

The picture gets fuzzier in the 19th century. Halema`uma`u was almost constantly active; its spill-outs built the caldera floor up more than 200 m (200 yards). At least eight other eruptions of Kilauea are known; by far the largest, along the east rift zone in 1840, had a volume of 0.2 cubic kilometers (260 million cubic yards).

Mauna Loa had at least 24 eruptions in the 19th century, more than in the 20th. It produced more than 2.5 cubic kilometers (3.3 billion cubic yards) of lava, almost certainly more than did Kilauea.

Hualalai, the third active volcano on the island, erupted in 1801. This flow underlies the north end of the runway at Keahole airport.

Precise dates of eruptions before 1823 are unknown, with one exception. At Kawaihae, John Young reportedly saw an eruption column issuing from Kilauea during explosions in November 1790. Aside from this, we must depend on geologic evidence to recognize deposits of past eruptions and to provide approximate ages for them.

The geologic record shows that Kilauea's summit area was very active during the first 500 years of the millennium, before the modern caldera formed. Many flows moved in all directions from the shield that capped the summit, some making it to the south coast.

The largest of these eruptions came from an off-center vent just east of Kilauea Iki. It produced the remarkable `Aila`au flow, which started in about 1410, lasted for some 60 years, and covered the area north of the east rift zone from Volcano to Kaloli Point.

Mauna Loa erupted about 80 times between the start of the millennium and 1832. Its eruptions impressed residents less than did those at Kilauea, probably because the activity was usually remote. Many of the eruptions must have been destructive, however, covering trails and destroying forests and cropland.

Two other volcanoes erupted in the last millennium before 1800. Hualalai had one or more eruptions in the late 1700s. East Maui volcano (Haleakala) erupted a flow into La Perouse Bay between about 1400 and 1600 by radiocarbon dating or shortly before 1790 by oral history.

Expect more of the same in the new millennium. Kilauea and Mauna Loa will be the show-offs, but Hualalai and East Maui will strut their stuff too. Now, if we live long enough to check this forecast...

Eruption Update

The surface flow activity on Pulama pali that we reported last week continued all week and provided visitors at the end of the Chain of Craters road in Hawai`i Volcanoes National Park with a spectacular view. Lava travels in a tube system from the vent at Pu`u `O`o to the top of Pulama pali, then breaks out of the tube and cascades down the pali. An eastern lobe of the flow destroyed another structure in the Royal Gardens subdivision this past week. Lava is pooling at the base of the pali and is slowly advancing toward the coast which is 2 km (1.2 mi) away.

No earthquakes were reported felt during the week ending on December 28.