Tuesday, April 2, 2013

Largest Earthquake in Hawaiʻi

Magnitude 7.9, Kaʻū, Island of Hawaiʻi, April 2, 1868

On March 27, 1868, whaling ships at Kawaihae on the west coast of Hawaiʻi observed dense clouds of smoke rising from Mauna Loa’s crater, Mokuʻāweoweo, to a height of several miles and reflecting the bright light from the lava pit.

Slight shocks were felt at Kona on the west coast and Kaʻū on the flanks of the volcano.

On the 28th, lava broke out on the southwest flank and created a 15-mile flow to the sea. Over 300 strong shocks were felt at Kaʻū and 50 to 60 were felt at Kona.

At Kilauea, the surface of the ground quivered for days with frequent vigorous shocks that caused lamps, crockery and chairs to spin around as if animated.

One shock resembled that of a cannon projectile striking the ground under the proprietor's bed, causing him to flee, according to the narrative published by C. H. Hitchcock in the Bulletin of the Seismological Society of America in 1912.

Between March 28, 1868 and April 11, over 2,000 distinct shocks were felt at Kona.

The main shocks struck on April 2, at 4:00 p.m., and again on April 4 at 12:30 a.m., the epicenter was located near Waiohinu.

“Thursday, April 2d, at a few minutes past four, p.m., the big earthquake occurred, which caused the ground around Kilauea to rock like a ship at sea. At that moment, there commenced fearful detonations in the crater, large quantities of lava were thrown up to a great height; portions of the wall tumbled in. This extraordinary commotion, accompanied with unearthly noise and ceaseless swaying of the ground continued from that day till Sunday night, April 5th”. (Hawaiian Gazette, May 6, 1868)

A magnitude of 7 ¾ was estimated for this earthquake (by Augustine Furumoto in his February 1966 article on the Seismicity of Hawaii in the Bulletin of the Seismological Society of America) based on the extent of intensity reports.  (Instrumental recordings, the usual basis for computing magnitudes, were not available at this early date.)

The shock was felt throughout the islands, as far as Niʻihau about 350 miles away.

The ground rolled like a ship at sea and many walls tumbled down.

A landslide three miles long and thirty feet thick swept down the hill carrying trees, animals, and men.  Thirty-one people and thousands of cattle, sheep, horses and goats were killed in the one slide.

A tsunami struck the coast from Hilo to South Cape, being most destructive at Keauhou, Puna and Honuʻapo; 180 houses were washed away and 62 lives were lost to the wave alone.

A 10-foot-high wave carried wreckage inland 800-feet. Not a house survived at Honuʻapo. A stone church and other buildings were destroyed at Punaluʻu.

Maximum wave heights were 65 feet, the highest observed on Hawaiʻi to date.

At Keauhou (now Keauhou Landing) the water rose 35-50-feet destroying all the houses and warehouses and drowning 46 people. At Hilo, the height of the wave was about 10-feet, and at Kealakekua, 6-feet. The tsunami also was observed on Maui and Oʻahu. Also felt on Lānaʻi, Maui, Oʻahu, and Kauaʻi.

“The tidal wave was much greater than before stated. It rolled in over the tops of the cocoanut trees, probably sixty feet high, and drove the floating rubbish, timber, etc., inland a distance of a quarter of a mile in some places, taking out to sea when it returned, houses, men, women, and almost everything movable. The villages Punaluu, Ninole, Kawaa and Honuapo were utterly annihilated.”  (American Journal of Science, 1868)

This major earthquake caused 77 deaths (tsunami, 46; landslide, 31).

It knocked almost all wooden houses off their foundations in the Keiawa, Punaluʻu and Nīnole areas. In those areas, straw houses supported by posts in the ground reportedly were “torn to shreds.”

At Kaʻū, the more substantial houses and every stone wall were thrown down.

At Waiʻōhinu, a large stone church collapsed within 10 seconds of the onset of shaking. The shock "ruined" the few stone buildings in Hilo and shook down almost every wall. Brooks became muddy.

At Kealakekua, strong trees were bent backward and forward "like reeds in a storm." Ground waves as much as 2-feet from ground to crest were observed at Kohala.

The motion was so violent at ʻUlupalakua that it was difficult for people to stand. Reports from Keaiwa and Kiolakaʻa suggest that vertical accelerations larger than 1g may have occurred (which means that the force of the earth pushing up on something is stronger than the force of gravity keeping it on the ground.)

Extensive surface effects were observed in the epicentral region. Ground fissures extended from Pahala to Kilauea. At Kahuku, a fissure about 5 kilometers long was reported. A volcanic eruption took place from that fissure a few days later, on April 7.

Along the Puna coast, the land subsided in places as much as 6-feet. At Kaimū, trees stood about 8-feet deep in sand and water. The plain at Kalapana sank about 6-feet, and water stood as much as 5-feet deep over 20 acres of formerly dry land.

Much of the information here is from USGS, with some noted from the diary and letters of Mrs. Sarah J. Lyman, wife of missionary David Layman in Hilo.

The image shows the map of the islands and the general location of Hawaiʻi’s largest earthquake.

© 2013 Hoʻokuleana LLC

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