Generated by Magnitude 7.2 Earthquake on November 29, 1975
House in Punalu`u demolished by tsunami related to
earthquake in November 1975
Photograph by David Shapiro, Honolulu Star-Bulletin
The largest tsunami generated locally in Hawai`i in the 20th century
was triggered by sudden, violent ground motion associated with the magnitude
7.2 earthquake on November 29, 1975. Waves reached 6 to 14 m above sea level
on the southeastern coast of the Big Island and generally less than 4 m
elsewhere on the island. The tsunami killed two people and caused property
damage of about $1.4 million (about $4.6 million in 1999 dollars).
The tsunami spread east and southwest from its source near Halape, 30 km
west of the earthquake epicenter. At Halape, the sea began slowly
rising within 10-30 seconds after ground shaking had diminished and then
rapidly developed into a rushing wave. At least two more large waves
of campers at Halape). No withdrawal of water was
observed before the initial wave. The tsunami reached Hilo in only 20 minutes,
Kailua-Kona in 27 minutes, and Honolulu in 49 minutes.
What is a tsunami?
A tsunami (tsoo-NAH-mee) is a series of waves of extremely long wave
length (distance between wave crests can be >100 km) generated
in the ocean by a disturbance that displaces the water. Tsunamis
are primarily associated with earthquakes in oceanic and coastal regions.
Landslides, volcanic eruptions, nuclear explosions, and even impacts of
objects from outer space (such as meteorites, asteroids, and comets) can
generate tsunamis. For more information about tsunamis see
from the University of Washington Geophysics Program and the
of tsunamis from the West Coast and Alaska Tsunami Warning Center.
About 50 tsunamis have been reported in the Hawaiian Islands
since the early 1800's. All but two (in 1975 and 1868) were
triggered by earthquakes located several thousand kilometers from
Hawai`i around the rim of the Pacific Ocean. The most damaging
tsunamis to hit the Big Island in this century occurred
in 1946 and 1960 and were caused by earthquakes located in
Alaska and Chile, respectively. Tsunamis from these distant earthquakes arrive
in the Hawaiian Islands 4 to 15 hours after the earthquake,
plenty of time for people to evacuate low-lying coastal
areas in the state.
1975 Tsunami Wave Heights
Highest waves from the tsunami reached 13.1 m above the shoreline at Keauhou
Landing (left) and 14.6 m at Halape (right).
Maximum heights of tsunami on Island of Hawai`i generated by the 7.2 earthquake on
November 29, 1975. Wave heights are given in meters relative to the postsubsidence
shoreline. Epicenter of the earthquake shown by star.
Damage Caused by the Tsunami
Damaged car, Punalu`u
Remains of warehouse, Honu`apo
Boat atop dock, Kona
Overturned boat, Hilo
Warning Time for a Locally Generated Tsunami:
Seconds to Minutes
The time between a large earthquake on the Island of
Hawai`i and arrival of first wave of a tsunami ranges
from less than a minute to as long as 15 to 25 minutes--generally too short to activate the Hawai`i
County Civil Defense warning system. The only practical
warning for such local events is the earthquake itself.
If ground shaking makes standing difficult, produces
significant rockfalls, and damages structures, one
should immediately move from low-lying coastal areas
to higher ground, ideally at least 12-15 m above sea
level. And because a tsunami consists of a series of
waves instead of a single wave, people are advised to
stay out of low-lying danger areas for several hours
after a large earthquake.
Tilling, R.I., Koyanagi, R.Y., Lipman, P.W., Lockwood, J.P., Moore, J.G., and Swanson, D.A.,
1976, Earthquake and related catastrophic events, Island of Hawaii, November 29,
1975: a preliminary report: U.S. Geological Survey Circular 740, 33 p.
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17 December 1998