Two weeks of terror in Ka‘u: the devastating events of 1868
March 1984 eruption. (USGS)
March marks the anniversary of the most recent eruption of Mauna Loa, which began March 25, 1984. It also reminds us of a much more destructive series of events that affected the island — the 16 days of earthquakes in 1868 that included a tsunami, landslide and eruption in Ka‘u.
As with many Mauna Loa eruptions, unusual activity was first observed at Mokuaweoweo, the volcano’s summit caldera. On Friday morning, March 27, 1868, people from Kawaihae to South Kona saw a column of smoke rising from the summit. Pele’s hair, lava filaments carried on the wind, confirmed a volcanic source of the smoke.
That evening, numerous earthquakes occurred, culminating in a strong and damaging earthquake early Saturday afternoon, March 28. By modern measure, this earthquake is estimated to have been about magnitude 7.
The earthquakes, which continued for days, were frequent and severe in Kona, Ka‘u and Hilo. Between 50 and 300 quakes were felt each day, with the most reported from Ka‘u. In some areas, it was described as nearly continuous ground motion.
The seismic activity came to a head on Thursday afternoon, April 2, when a violent earthquake — at least magnitude 7.9 — rattled the island and beyond. Located beneath South Hawaii, the quake was felt as far away as Kauai and stopped clocks on Oahu.
In Ka‘u, the destruction was nearly complete. People who had been standing or on horseback were knocked to the ground. Those sitting on the ground had to brace themselves with their hands and feet to remain upright as the powerful shaking went on for several minutes. All stone structures — buildings and walls — were thrown down.
The shaking caused several landslides in Ka‘u, within Kilauea caldera, in Hilo and along the Hamakua coast. The collapse of a cliff in Hilo caused one death, and a large mud slide in Wood Valley north of Pahala buried 31 people in a matter of minutes.
As the people of Ka‘u were recovering from the earthquake, they noticed the ocean receding from the coastline. Over the next several hours, at least eight waves washed ashore, razing coastal villages and carrying people and animals into the sea. The tsunami, estimated to be more than 20 feet high in Ka‘u, caused damage from South Point, Kalae, to Cape Kumukahi, Kapoho, destroying more than 100 structures and taking 47 lives. The tsunami was detected several hours later on the west coast of the United States.
But the devastation was not over. Strong earthquakes continued to shake the island. On Tuesday evening, April 7, a fissure opened low on the southwest rift zone of Mauna Loa, disgorging voluminous amounts of lava. The lava fountains jetted to heights of several hundred yards and produced lava flows that rushed southward to the sea — a distance of 8 miles — in 3.5 hours. The fountains also produced copious amounts of tephra that blanketed Ka‘u with deposits of cinder and Pele’s hair several inches deep. Vog shrouded the islands of Hawaii, Maui and Oahu.
The lava flow was inactive by Saturday, April 11, and the earthquakes, though less frequent, were still occurring at a rate of two to three per day several months later. In fact, recent studies suggest that we are still recording aftershocks of the 1868 main shock.
Using modern analysis, scientists have hypothesized that the southeastern part of the island, from Kapoho to Kalae, moved seaward and subsided several feet during the April 2, 1868, earthquake.
At the time, American missionaries and Hawaiians said there was no record of such devastating events in the history of the islands. But the geologic processes that caused the 1868 events continue to produce similar, less devastating, movements of the island’s southeast flank in the form of large earthquakes, such as the magnitude 7.7 Kalapana quake in 1975 and the steady seaward creep of Kilauea’s south flank.
HVO continues to track these movements and study historical events, like the 1868 Ka‘u earthquakes, landslides, tsunami and eruption, for the clues they provide for our future.
Kilauea activity update
A lava lake within Halemaumau produced nighttime glow visible via HVO’s webcam during the past week. The lava level fluctuated between 148 and 167 feet below the rim of the Overlook crater.
On Kilauea’s east rift zone, the Kahaualea 2 flow continued to be active northeast of Puu Oo. The active flow front was 5.1 miles northeast of the vent on Puu Oo on March 21. Webcam images indicate that small, lava-sparked forest fires continue to burn.
There were three felt earthquakes in the past week on Hawaii Island. At 4:56 p.m. March 20, a magnitude 3.4 earthquake occurred 4.5 miles southeast of Puu Oo Crater at a depth of 5 miles. At 7:10 a.m. March 22, a magnitude 2.4 earthquake occurred 2.4 miles northwest of Opihikao at a depth of 2.4 miles. At 8:05 p.m. Tuesday, a magnitude 2.5 earthquake occurred 2.5 miles northeast of Honaunau at a depth of 8.2 miles.
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