Volcano Watch: Remembering the destructive Kalapana earthquake 50 years ago
Fifty years ago this month, the largest 91直播 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 Nov. 29, 1975.
Named the “Kalapana earthquake” for its epicenter near the town of Kalapana on the southeast side of the Island of 91直播, 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. on Nov. 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 Halape, on the south coast in 91直播 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 91直播, with waves that damaged docks and piers, stranded and sunk boats, demolished homes and businesses in Punalu‘u, and flooded Ali‘i Drive in Kona. The highest wave reached an estimated 48 feet (14.6 m) above the shoreline east of Halap, 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.
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 91直播 more than five hours after the earthquake, giving time for evacuation of coastal zones.
In 91直播, 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 91直播, from Honu‘apo to Kaimu, 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.
Kilauea had been at a high level of inflation in November 1975 and the earthquake also triggered a small volume and brief eruption within Kaluapele, Kilauea’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 91直播, 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 Kilauea’s south flank, and hazards associated with its movement, have changed since 1975. And on Saturday, Nov. 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/.
Volcano activity updates
Kilauea has been erupting episodically within the summit caldera since Dec. 23, 2024. Its USGS Volcano Alert level is WATCH.
Episode 36 lava fountaining happened for five hours on Sunday, Nov. 4. Glow from the vents was observed over the past week during nighttime hours. The summit is reinflating and forecasting models indicate that episode 37 is likely to start between November 21 and 26. No unusual activity has been noted along Kilauea’s East Rift Zone or Southwest Rift Zone.
Mauna Loa is not erupting. Its USGS Volcano Alert Level is at NORMAL.
No earthquakes were reported felt in the 91直播an Islands during the past week.
Please visit HVO’s website for past Volcano Watch articles, Kilauea and Mauna Loa updates, volcano photos, maps, recent earthquake information, and more. Email questions to askHVO@usgs.gov.
