This significant geological formation, colloquially referred to as Maka Lahi, signifying ‘Big Rock,’ was displaced approximately 7,000 years ago by the immense force of a tsunami, which carried it inland for a distance exceeding 200 meters.
The limestone boulder Maka Lahi. Image credit: Köhler et al., doi: 10.1016/j.margeo.2025.107567.
The Maka Lahi boulder presents impressive dimensions, measuring 14 x 12 x 6.7 meters and possessing an estimated mass of nearly 1,200 tons. These characteristics establish it as the preeminent known boulder situated atop a cliff and rank it among the most substantial wave-transported boulders documented globally.
This colossal limestone structure is situated inland, approximately 200 meters from the current shoreline along the southern periphery of Tongatapu, an island nation in Tonga.
Martin Köhler, a doctoral candidate at the University of Queensland, recounted the discovery, stating, “Our team had been engaged in surveying the southern sector of Tongatapu, meticulously examining the coastal cliffs for indications of historical tsunami activity.”
“As the day was drawing to a close,” Köhler continued, “we conversed with some local farmers who then drew our attention to this remarkable boulder.”
“The revelation truly astonished me; its placement far inland, beyond the scope of our planned fieldwork, strongly implied traversal by an exceptionally powerful tsunami.”
“Witnessing this enormous rock formation, partially obscured and enfolded by abundant vegetation, was a profoundly surreal experience.”
“Following the creation of a three-dimensional model, we returned to the coastline to pinpoint the probable origin of the boulder, identifying a location on a cliff face situated more than 30 meters above sea level.”
Through sophisticated numerical simulations, the researchers determined that wave crests of approximately 50 meters, sustained for roughly 90 seconds, would have been requisite to dislodge the Maka Lahi boulder from its original precipice and transport it to its present position.
Dr. Annie Lau, a distinguished coastal geomorphologist affiliated with the University of Queensland, elaborated on the region’s geological context. “Tonga has a protracted history of tsunami events, frequently instigated by seismic activity and volcanic eruptions along the submerged Tofua Ridge and within the Tonga Trench,” she explained.
“The most recent tsunami to impact Tonga in 2022 resulted in six fatalities and inflicted considerable widespread devastation.”
“A comprehensive understanding of past cataclysmic events is absolutely indispensable for contemporary disaster preparedness and for effective risk assessment, both presently and in the future.”
“The insights gleaned from our investigation of the Maka Lahi boulder provide tangible evidence of a significant tsunami event within the Pacific region during the Holocene epoch, which commenced approximately 11,700 years ago.”
“This detailed analysis serves to enhance our comprehension of how waves transport geological debris, thereby contributing to more robust coastal hazard assessments in tsunami-prone areas globally.”
The comprehensive research findings detailing this discovery have been disseminated in the peer-reviewed journal Marine Geology, accessible via the provided link.
Martin Köhler et al. 2025. Discovery of the world’s largest cliff-top boulder: Initial insights and numerical simulation of its transport on a 30-40 m high cliff on Tongatapu (Tonga). Marine Geology 487, 107567; doi: 10.1016/j.margeo.2025.107567
