Scientists have made an unexpected discovery off the coast of Hawaii
The Hawaiian Islands owe their existence to a gigantic flow of molten material rising from the Earth’s depths. For a long time, scientists believed that such ‘hotspots’ gradually cooled down.
However, a new study has revealed something unexpected: over the past 47 million years, the Hawaiian hotspot has, in fact, become approximately 250 °C hotter.
The study has been published in the journal *Earth and Planetary Science Letters*.
What the scientists discovered
The researchers analysed lava samples from 16 ancient and modern volcanoes in the Hawaiian island chain.
Using a new geochemical method to estimate magma temperature, they reconstructed how hot the material rising from the Earth’s depths was during different geological periods.
It turned out that the temperature of the mantle plume — a vast flow of molten material beneath Hawaii — did not decrease, as many geologists had assumed, but gradually increased.
What is a ‘hotspot’?
The Hawaiian Islands are not situated at the boundary of lithospheric plates, as are most of the Earth’s volcanoes.
They formed above a so-called ‘hotspot’ – a place where molten material constantly rises from the depths of the mantle. As the Pacific Plate moves slowly, new volcanoes form one after another above this source, creating a long chain of islands.
Why some volcanoes turned out to be gigantic
Research has shown that over the last tens of millions of years, there have been two periods of particularly intense heating.
It is these, according to scientists, that led to the formation of the largest volcanoes in the entire Hawaiian chain.
One of them — Pūhāhonu — is considered the largest shield volcano to have formed on Earth in the last 60 million years.
The second period of heating is linked to the formation of the modern Hawaiian Islands.
Why this is important
The discovery challenges our understanding of how mantle plumes — giant updrafts of hot material within the Earth — behave.
It was previously thought that they gradually cooled over time. New data suggest that, at least in the case of Hawaii, the process may have been the opposite.
The researchers suggest that this was caused by the movement of particularly hot and dense material in the deepest layers of the mantle.
What this means for science
A new method for measuring the temperature of ancient magma will help to reconstruct the history of volcanism more accurately, not only in Hawaii but also in other regions of the planet.
The authors believe this will provide a better understanding of why some volcanoes remain relatively small, whilst others grow into true giants.
Background
The Hawaiian island chain consists of approximately 65 volcanoes that have formed over the last 47 million years as the Pacific lithospheric plate has moved over the same hotspot.
It is this natural ‘conveyor belt’ that created the Hawaiian Islands, which continue to grow to this day.
Source
Michael O. Garcia et al. Taking the temperature of the Hawaiian plume using multiple geochemical approaches: Evidence for secular heating from 47 Ma to the present. Earth and Planetary Science Letters (2026).