The Hawaiian Islands are the visible peaks of an immense, mostly submerged mountain range stretching thousands of miles across the Pacific Ocean. Unlike most global volcanism caused by colliding tectonic plates, these islands owe their existence to a unique and persistent geological feature known as a hotspot. This hotspot provides a steady source of magma beneath the ocean floor, building islands sequentially for millions of years and creating a distinct chain that holds the answer to where the next island will form.
How the Hawaiian Hotspot Works
The process begins with a stationary plume of extremely hot rock, called a mantle plume, rising from deep within the Earth’s mantle. Scientists refer to this feature as the Hawaiian Hotspot. This plume acts like a fixed torch, supplying magma to the surface by burning a hole through the oceanic crust above it.
The Pacific Plate, which forms the ocean floor, constantly moves over the hotspot in a northwesterly direction. As the plate slowly shifts, the active magma source remains in place, periodically punching through the crust to build a new volcano. Once a newly formed volcano moves away from the plume’s heat source, its magma supply is cut off, and it becomes extinct.
This continuous movement explains why the islands are progressively older and more eroded the further they are from the Big Island of Hawaiʻi. The island currently positioned directly over the hotspot is the youngest and most volcanically active. The Pacific Plate drifts at a rate of approximately 5 to 10 centimeters (2 to 4 inches) per year, carrying the entire volcanic chain with it.
The Birth of the Next Island
The next Hawaiian island is forming southeast of the Big Island of Hawaiʻi, directly over the active magma plume. This future island is already a massive, actively growing submarine volcano known as Kamaʻehuakanaloa Seamount, formerly called Lōʻihi. It is located about 35 kilometers (22 miles) off the south coast of the Big Island and represents the newest volcano in the entire chain.
Kamaʻehuakanaloa Seamount stands more than 3,000 meters (10,000 feet) tall above the surrounding seafloor. However, its summit remains submerged about 975 meters (3,200 feet) below the ocean surface. Scientific monitoring confirms its active status, often recording intense earthquake swarms, such as the 1996 event that involved over 4,000 tremors. These seismic events indicate the movement of magma and the restructuring of the volcano’s flanks.
The seamount is currently in its preshield stage, characterized by steep slopes and less frequent eruptions compared to a mature shield volcano like Kīlauea. Scientists estimate that Kamaʻehuakanaloa will need to accumulate several hundred cubic kilometers of lava before it breaches the surface. Based on historical growth rates, the summit is projected to emerge above sea level sometime in the next 10,000 to 100,000 years.
The Fate of the Volcanic Chain
As each island moves off the hotspot, its growth cycle ends and volcanism ceases. The island then begins to undergo two major geological processes: erosion and subsidence. The shield volcanoes are composed of basalt, a porous rock easily worn away by wind, rain, and powerful ocean waves.
The enormous weight of the volcano causes the underlying oceanic crust to slowly sink into the mantle, a process called subsidence. Furthermore, the seafloor cools as it moves away from the heat of the hotspot, becoming denser and contributing to the island’s gradual descent. These forces cause the islands to shrink over millions of years.
The older islands of the Northwestern Hawaiian Islands demonstrate this fate, transitioning from high volcanic peaks to low-lying atolls like Midway. Eventually, all that remains of the massive mountain is a flat-topped, submerged structure known as a guyot or seamount, as seen in the distant Emperor Seamounts. This chain of underwater mountains serves as a record of the Pacific Plate’s movement and the ultimate destiny of every Hawaiian island.