Remembering the destructive Kalapana earthquake 50 years ago — USGS Volcano Watch

Fifty years ago this month, the largest Hawaii earthquake of the 20th and 21st centuries occurred. Earthquake shaking, as well as ground subsidence and local tsunami, contributed to a catastrophic sequence of events on November 29, 1975.

Road damage in Hawaiʻi Volcanoes National Park caused by the magnitude-7.7 earthquakes on November 29, 1975. USGS image. 

Named the “Kalapana earthquake” for its epicenter near the town of Kalapana on the southeast side of the Island of Hawaiʻi, the earthquake occurred about 5 miles (9 km) beneath ground surface. It was preceded by small foreshocks, several in the magnitude-4-to-5 range, that started a month before the mainshock. The largest foreshock was a magnitude-5.7 earthquake at 3:36 a.m. HST on November 29, 1975.

Just over an hour later, at 4:48 a.m., the magnitude-7.7 struck. Shaking lasted more than 30 seconds and was felt across the island and as far as Maui and Oahu. The earthquake caused an estimated $2.7 million in damages, mostly in Hilo, and included cracks in roads, water pipes, and walls, toppled chimneys, collapsed water tanks, rockwalls, and fences, broken windows, and materials on shelves falling and breaking.

More damaging than the earthquake was the fatal tsunami that swept the island’s shores shortly afterwards. Campers at Halapē, on the south coast in Hawaiʻi Volcanoes National Park, were awakened by the shaking and by rockfalls from the pali above that the shaking triggered. 

As recorded in a USGS report detailing the survivor accounts, the campers recognized that a tsunami could follow the earthquake. They saw the ocean noticeably rising and quickly fled for higher ground, but the water overtook them. Most of the campers were swept into a crack, where one described the several tsunami waves as feeling like being inside a washing machine. The water receded about 10 minutes after the earthquake. One camper was swept out and never found; another was drowned or battered to death by the waves; seven others were hospitalized afterwards.

The tsunami wrapped around the Island of Hawaiʻi, with waves that damaged docks and piers, stranded and sunk boats, demolished homes and businesses in Punaluʻu, and flooded Aliʻi Drive in Kona. The highest wave reached an estimated 48 feet (14.6 m) above the shoreline east of Halapē, leaving a line of vegetation, rocks, and other debris. In total, the tsunami caused an estimated $1.4 million in damages, for a total of $4.1 million in damages from the earthquake and tsunami combined.

The submerged coconut grove at Halapē, in Hawaiʻi Volcanoes National Park, marks the former coastline that was submerged during the ground movement associated with the November 29, 1975, magnitude-7.7 earthquake. USGS image. 

Tsunami waves arrived in Hilo just 20 minutes after the earthquake occurred. This is much quicker than tsunami generated by distant earthquakes, such as on July 29, 2025, when a magnitude-8.8 earthquake struck the Kamchatka Peninsula, Russia. The Pacific Tsunami Warning Center forecast that tsunami waves from the Kamchatka earthquake would arrive in Hawaii more than five hours after the earthquake, giving time for evacuation of coastal zones. 

In Hawaii, when you feel strong shaking, that is the warning for a potential tsunami and people near the coast should immediately head for higher ground. If a local tsunami is generated, it will arrive quickly, possibly before any sirens can be sounded or emergency messages can be issued. 

Whether or not a local tsunami is generated depends on if there is significant vertical submarine ground movement associated with the earthquake.  In 1975, areas along the south coast of the Island of Hawaiʻi, from Honuʻapo to Kaimū, moved as much as 26 feet (8 m) horizontally and subsided by as much as 11.5 feet (3.5 m), submerging vegetation and inundating the former coastline.  The earthquake also produced extensive cracks on a 15 mile (25 km) stretch of the Hilina fault system, with up to 5 feet (1.5 m) of vertical offset. 

Kīlauea had been at a high level of inflation in November 1975 and the earthquake also triggered a small volume and brief eruption within Kaluapele, Kīlauea’s summit caldera. The eruption began less than an hour after the earthquake and was over within 24 hours. 

While lava flows and fountains often change topography of portions of the Island of Hawaiʻi, less-frequent large earthquakes and ground movements have the potential to reshape the coastline and cause damage over larger areas. For more information about earthquake preparedness, check out https://www.shakeout.org/hawaii/. In next week's article, we’ll learn about how our understanding and monitoring of Kīlauea’s south flank, and hazards associated with its movement, have changed since 1975. And on Saturday, November 29, the Pacific Tsunami Museum in Hilo will be hosting a series of special events to remember the events of that day 50 years ago; learn more here: https://tsunami.org/events/. 

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Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.