The Hawaiian Islands are a vast chain of volcanic landmasses rising from the deep Pacific Ocean floor. Unlike most volcanoes, which form where tectonic plates meet, this archipelago is located far from any plate edge, in the middle of the Pacific Plate. The powerful natural force responsible for creating this unique mid-ocean chain is a stationary column of intensely hot rock known as a mantle plume, which creates a phenomenon called a hotspot.
The Hotspot Mechanism
The concept of a hotspot describes a persistent, fixed source of heat that originates deep within the Earth, likely rising from the boundary between the core and the mantle. This deep-seated thermal anomaly pushes a column of unusually hot material—the mantle plume—upward through the mantle toward the surface. The plume’s relative immobility over millions of years allows it to act as a consistent volcanic punch through the overlying crust.
As this superheated rock nears the surface, the pressure surrounding it significantly decreases, causing the solid rock to melt without additional temperature increase, a process called decompression melting. This molten rock, or magma, then accumulates and ascends through the oceanic crust, eventually erupting onto the seafloor. This volcanism produces large, broad shield volcanoes built from effusive, low-viscosity basaltic lava flows.
The Hawaiian hotspot is highly productive and long-lived, generating an immense volume of magma over geologic time. This explains why the islands are among the largest volcanic structures on Earth, forming a massive submarine mountain range. The uplift caused by the buoyant plume also creates a noticeable rise in the seafloor surrounding the islands, known as the Hawaiian Swell.
Creating the Island Chain
The formation of the Hawaiian Islands is a two-part process involving the stationary mantle plume and the continuous movement of the Pacific tectonic plate. The crust of the Pacific Plate acts like a conveyor belt, slowly sliding over the relatively fixed hotspot in a northwesterly direction. This movement is estimated to be approximately 3.5 inches per year, a rate roughly comparable to the speed at which human fingernails grow.
A volcano that forms directly over the plume’s center receives a constant supply of magma, allowing it to grow large enough to break the ocean surface and become an island. As the Pacific Plate carries the newly formed island away from the heat source, the volcano is cut off from its magma supply and its activity ceases. The hotspot continues to generate heat and magma, beginning the process of building a new volcano on the crust directly above it.
This cycle of creation and transport results in a linear chain of volcanoes that records the plate’s movement over the plume across millions of years. The islands and seamounts in the chain show a clear age progression, becoming progressively older, smaller, and more eroded the farther they are located to the northwest. The oldest submerged volcanoes in the extended Hawaiian–Emperor seamount chain are nearly 70 million years old.
The Active and Future Islands
The current location of the hotspot is beneath the southeastern end of the chain, centered on the Island of Hawaiʻi, often called the Big Island. This island is consequently the youngest and largest in the archipelago, still actively growing due to the magma supply from the plume. The Big Island is home to several active volcanoes, including Mauna Loa, the largest shield volcano on Earth by volume, and Kilauea, one of the world’s most consistently active volcanoes.
The process of island formation is ongoing, and the next landmass in the chain is already being built beneath the ocean surface. Located about 22 miles southeast of the Big Island is the Kamaʻehuakanaloa Seamount, an active submarine volcano that represents the future of the island chain. The summit of this massive underwater mountain currently sits about 3,200 feet below sea level.
Kamaʻehuakanaloa is expected to continue erupting and building upon itself over the coming millennia. Scientists estimate that the seamount will eventually emerge above the surface of the Pacific, becoming the next visible Hawaiian island, likely in the next 10,000 to 100,000 years. Eventually, the Big Island will also be carried away by the moving Pacific Plate, its volcanoes will become dormant, and the process will continue with the next landmass forming over the fixed, deep-earth heat source.